Urinary stress incontinence and other maternal outcomes 2 years after caesarean or vaginal birth for twin pregnancy: a multicentre randomised trial.

OBJECTIVE: Does planned caesarean compared with planned vaginal birth lower the risk of problematic urinary stress, faecal, or flatal incontinence? DESIGN: Women between 320/7 and 386/7 weeks of gestation with a twin pregnancy were randomised to planned caesarean or planned vaginal birth. SETTING: The trial took place at 106 centres in 25 countries. POPULATION: A total of 2305 of the 2804 women enrolled in the study completed questionnaires at 2 years (82.2% follow-up): 1155 in the planned caesarean group and 1150 in the planned vaginal birth group. METHODS: A structured self-administered questionnaire completed at 2 years postpartum. MAIN OUTCOME MEASURES: The primary maternal outcome of the Twin Birth Study was problematic urinary stress, or fecal, or flatal incontinence at 2 years RESULTS: Women in the planned caesarean group had lower problematic urinary stress incontinence rates compared with women in the planned vaginal birth group [93/1147 (8.11%) versus 140/1143 (12.25%); odds ratio, 0.63; 95% confidence interval, 0.47-0.83; P = 0.001]. Among those with problematic urinary stress incontinence, quality of life (measured using the Incontinence Impact Questionnaire, IIQ-7) was not different for planned caesarean versus planned vaginal birth groups [mean (SD): 18.4 (21.0) versus 19.1 (21.5); P = 0.82]. There were no differences in problematic faecal or flatal incontinence, or in other maternal outcomes. CONCLUSIONS: Among women with a twin pregnancy and no prior history of urinary stress incontinence, a management strategy of planned caesarean compared with planned vaginal birth reduces the risk of problematic urinary stress incontinence at 2 years postpartum. Our findings show that the prevalence but not the severity of urinary stress incontinence was associated with mode of birth. FUNDING: Canadian Institutes of Health Research (CIHR) (grant no. MCT-63164). TWEETABLE ABSTRACT: For women with twins, planned caesarean compared with planned vaginal birth is associated with decreased prevalence but not severity of urinary stress incontinence at 2 years.

Control of Hypertension In Pregnancy Study randomised controlled trial-are the results dependent on the choice of labetalol or methyldopa?

OBJECTIVE: To determine whether the difference in outcomes between 'less tight' (target diastolic blood pressure [dBP] of 100 mmHg) versus 'tight' control (target dBP of 85 mmHg) in the CHIPS Trial (ISRCTN 71416914, http://pre-empt.cfri.ca/;CHIPS) depended on the choice of labetalol or methyldopa, the two most commonly used antihypertensive agents in CHIPS. DESIGN: Secondary analysis of CHIPS Trial data. SETTING: International multicentre randomised controlled trial (94 sites, 15 countries). POPULATION OR SAMPLE: A total of 987 women with non-severe non-proteinuric pregnancy hypertension. METHODS: Logistic regression was used for comparisons of 'less tight' versus 'tight' control among women treated with labetalol (but not methydopa) versus methyldopa (but not labetalol). Analyses were adjusted for the influence of baseline factors, including use of any antihypertensive therapy at randomisation. MAIN OUTCOME MEASURES: Main CHIPS Trial outcomes: primary (perinatal loss or high-level neonatal care for > 48 hours), secondary (serious maternal complications), birthweight < 10th centile, severe maternal hypertension, pre-eclampsia, and delivery at < 34 or < 37 weeks. RESULTS: Of 987 women in CHIPS, antihypertensive therapy was taken by 566 women at randomisation (labetalol 111 ['less tight'] versus 127 ['tight'] or methyldopa 126 ['less tight'] versus 117 ['tight']) and 815 women after randomisation (labetalol 186 ['less tight'] versus 247 ['tight'] and methyldopa by 98 ['less tight'] versus 126 ['tight']). Following adjustment, odds ratios for outcomes in 'less tight' versus 'tight' control were similar between antihypertensive groups according to 'at randomisation' and 'after randomisation' therapy. CONCLUSION: Outcomes for 'less tight' versus 'tight' control were not dependent on use of methyldopa or labetalol. TWEETABLE ABSTRACT: In the CHIPS Trial, maternal and infant outcomes were not dependent on use of labetalol or methyldopa.

Do labetalol and methyldopa have different effects on pregnancy outcome? Analysis of data from the Control of Hypertension In Pregnancy Study (CHIPS) trial.

OBJECTIVE: To compare pregnancy outcomes, accounting for allocated group, between methyldopa-treated and labetalol-treated women in the CHIPS Trial (ISRCTN 71416914) of 'less tight' versus 'tight' control of pregnancy hypertension. DESIGN: Secondary analysis of CHIPS Trial cohort. SETTING: International randomised controlled trial (94 sites, 15 countries). POPULATION OR SAMPLE: Of 987 CHIPS recruits, 481/566 (85.0%) women treated with antihypertensive therapy at randomisation. Of 981 (99.4%) women followed to delivery, 656/745 (88.1%) treated postrandomisation. METHODS: Logistic regression to compare outcomes among women who took methyldopa or labetalol, adjusted for the influence of baseline factors. MAIN OUTCOME MEASURES: CHIPS primary (perinatal loss or high level neonatal care for >48 hours) and secondary (serious maternal complications) outcomes, birthweight <10th centile, severe maternal hypertension, pre-eclampsia and delivery at <34 or <37 weeks. RESULTS: Methyldopa and labetalol were used commonly at randomisation (243/987, 24.6% and 238/987, 24.6%, respectively) and post-randomisation (224/981, 22.8% and 433/981, 44.1%, respectively). Following adjusted analyses, methyldopa (versus labetalol) at randomisation was associated with fewer babies with birthweight <10th centile [adjusted odds ratio (aOR) 0.48; 95% CI 0.20-0.87]. Methyldopa (versus labetalol) postrandomisation was associated with fewer CHIPS primary outcomes (aOR 0.64; 95% CI 0.40-1.00), birthweight <10th centile (aOR 0.54; 95% CI 0.32-0.92), severe hypertension (aOR 0.51; 95% CI 0.31-0.83), pre-eclampsia (aOR 0.55; 95% CI 0.36-0.85), and delivery at <34 weeks (aOR 0.53; 95% CI 0.29-0.96) or <37 weeks (aOR 0.55; 95% CI 0.35-0.85). CONCLUSION: These nonrandomised comparisons are subject to residual confounding, but women treated with methyldopa (versus labetalol), particularly those with pre-existing hypertension, may have had better outcomes. TWEETABLE ABSTRACT: There was no evidence that women treated with methyldopa versus labetalol had worse outcomes.

Maternal outcomes at 3 months after planned caesarean section versus planned vaginal birth for twin pregnancies in the Twin Birth Study: a randomised controlled trial.

OBJECTIVE: To compare outcomes at 3 months post partum for women randomised to give birth by planned caesarean section (CS) or by planned vaginal birth (VB) in the Twin Birth Study (TBS). DESIGN: We invited women in the TBS to complete a 3-month follow-up questionnaire. SETTING: Two thousand and eight hundred and four women from 25 countries. POPULATION: Two thousand and five hundred and seventy women (92% response rate). METHODS: Women randomised between 13 December 2003 and 4 April 2011 in the TBS completed a questionnaire and outcomes were compared using an intention-to-treat approach. MAIN OUTCOME AND MEASURES: Breastfeeding, quality of life, depression, fatigue and urinary incontinence. RESULTS: We found no clinically important differences between groups in any outcome. In the planned CS versus planned VB groups, breastfeeding at any time after birth was reported by 84.4% versus 86.4% (P = 0.13); the mean physical and mental Short Form (36) Health Survey (SF-36) quality of life scores were 51.8 versus 51.6 (P = 0.65) and 46.7 versus 46.0 (P = 0.09), respectively; the mean Multidimensional Assessment of Fatigue score was 20.3 versus 20.8 (P = 0.14); the frequency of probable depression on the Edinburgh Postnatal Depression Scale was 14.0% versus 14.8% (P = 0.57); the rate of problematic urinary incontinence was 5.5% versus 6.4% (P = 0.31); and the mean Incontinence Impact Questionnaire-7 score was 20.5 versus 20.4 (P = 0.99). Partner relationships, including painful intercourse, were similar between the groups. CONCLUSION: For women with twin pregnancies randomised to planned CS compared with planned VB, outcomes at 3 months post partum did not differ. The mode of birth was not associated with problematic urinary incontinence or urinary incontinence that affected the quality of life. Contrary to previous studies, breastfeeding at 3 months was not increased with planned VB. TWEETABLE ABSTRACT: Planned mode of birth for twins doesn't affect maternal depression, wellbeing, incontinence or breastfeeding.

Thyroid cancer patients' involvement in adjuvant radioactive iodine treatment decision-making and decision regret: an exploratory study.

PURPOSE: We explored regret in thyroid cancer patients, relating to the decision to accept or reject adjuvant radioactive iodine treatment. METHODS: We studied patients with a recent diagnosis of early stage papillary thyroid carcinoma, in whom treatment decisions on adjuvant radioactive iodine had been finalized. Participants completed a Decision Regret Scale questionnaire. We asked the participants to identify who made the final decision about radioactive iodine treatment. We explored the relationship between decision regret and a) degree of patient involvement in decision-making and b) receipt of radioactive iodine treatment. RESULTS: We included 44 individuals, more than half of whom received adjuvant radioactive iodine treatment (26/44). Decision regret was generally low (mean 22.1, standard deviation [SD] 13.0). Participants reported that the final treatment decision was made by the following: patient and doctor (52.3%, 23/44), completely the patient (27.3%, 12/44), or completely the physician (20.5%, 9/44). Decision regret significantly differed according to who made the final decision: the patient (mean 19.0, SD 11.3), patient and doctor (mean 19.5, SD 7.4), and the doctor (mean 32.9, SD 20.37) (F = 4.569; degrees of freedom = 2, 41; p = 0.016). There was no significant difference in decision regret between patients who received radioactive iodine and those who did not (mean difference -2.5; 95% confidence interval -10.6, 5.6; p = 0.540). CONCLUSION: Thyroid cancer patients who reported being involved in the final treatment decision on adjuvant radioactive iodine had less regret than those who did not.

How can we meet the information needs of patients with early stage papillary thyroid cancer considering radioactive iodine remnant ablation?

In patients with early stage papillary thyroid carcinoma (PTC) who have had a thyroidectomy, the decision must be made to accept or reject radioactive iodine remnant ablation (RRA). Counselling patients about this decision can be challenging, given the medical evidence uncertainties and the complexity of related information. Although physicians are the primary source of medical information for patients considering RRA, some patients have a desire for supplemental information from sources such as the internet. Yet, thyroid cancer resources on the internet are of variable quality, and some may not be applicable to the individual case. We have developed a computerized educational tool [called a decision aid (DA)], directed to patients with early stage papillary thyroid cancer, and intended as an adjunct to physician counselling, to relay evidence-based medical information on disease prognosis and the choice to accept or reject RRA. DAs are tools used to inform patients about available treatment options and have been utilized in oncologic decision-making. We tested our web-based DA in fifty patients with early stage PTC and found that it improved medical knowledge. Furthermore, participants found the technical usability of the tool acceptable. We are currently conducting a randomized controlled trial comparing the use of the DA plus usual care to usual care alone to confirm the educational benefit of the website and examine its impact on the decision-making process. In the future, DAs may play an expanded role as an adjunct to physician counselling in the care of patients with thyroid cancer.

The Early External Cephalic Version (ECV) 2 Trial: an international multicentre randomised controlled trial of timing of ECV for breech pregnancies.

OBJECTIVE: To investigate whether initiating external cephalic version (ECV) earlier in pregnancy might increase the rate of successful ECV procedures, and be more effective in decreasing the rate of non-cephalic presentation at birth and of caesarean section. DESIGN: An unblinded multicentred randomised controlled trial. SETTING: A total of 1543 women were randomised from 68 centres in 21 countries. POPULATION: Women with a singleton breech fetus at a gestational age of 33(0/7) weeks (231 days) to 35(6/7) weeks (251 days) of gestation were included. METHODS: Participants were randomly assigned to having a first ECV procedure between the gestational ages of 34(0/7) (238 days) and 35(6/7) weeks of gestation (early ECV group) or at or after 37(0/7) (259 days) weeks of gestation (delayed ECV group). MAIN OUTCOME MEASURES: The primary outcome was the rate of caesarean section; the secondary outcome was the rate of preterm birth. RESULTS: Fewer fetuses were in a non-cephalic presentation at birth in the early ECV group (314/765 [41.1%] versus 377/768 [49.1%] in the delayed ECV group; relative risk [RR] 0.84, 95% CI 0.75, 0.94, P=0.002). There were no differences in rates of caesarean section (398/765 [52.0%] versus 430/768 [56.0%]; RR 0.93, 95% CI 0.85, 1.02, P=0.12) or in risk of preterm birth (50/765 [6.5%] versus 34/768 [4.4%]; RR 1.48, 95% CI 0.97, 2.26, P=0.07) between groups. CONCLUSION: External cephalic version at 34-35 weeks versus 37 or more weeks of gestation increases the likelihood of cephalic presentation at birth but does not reduce the rate of caesarean section and may increase the rate of preterm birth.

It's a choice to move forward: women's perceptions about treatment decision making in recurrent ovarian cancer.

OBJECTIVE: This research explores the treatment decision-making (TDM) experiences of women with recurrent ovarian cancer (ROC) with regard to treatment options; their understanding of risks and benefits of various treatment options; the decision-making role they want for themselves and for their oncologist; and the social context of the consultation as it pertains to the decision. METHODS: We conducted semi-structured interviews with 26 women at the time of first recurrence. Through inductive data analysis key themes were identified. RESULTS: Many women describe self-identifying the cancer recurrence fairly quickly due to new symptoms. Many feel that the goal for treating their recurrence is to control versus cure the cancer. They describe the subsequent process of diagnosis and TDM for ROC as quick and straightforward with all women accepting the oncologists' treatment recommendation. They feel that the type and number of treatment options are limited. They have a strong desire for physician continuity in their care. Participants feel that their doctor's recommendations as well as their previous experience with ovarian cancer are strong factors influencing their current TDM process. CONCLUSIONS: Shared decision making is based on a simultaneous participation of both the physician and patient in TDM. When faced with ROC, women feel that their doctor's recommendation and their past experience with treatment and TDM are prominent factors influencing the current TDM process.

Effect of evapotranspiration on the salinity of wastewater treated by aquatic plants.

The shortage of good quality water resources is becoming an important issue in arid and semi-arid zones. Irrigation systems must be developed that are capable of delivering low quality wastewater while taking into account environmental and health requirements. For this reason, the availability of water resources of marginal quality, such as desalinated wastewater, can be a significant contribution to the water supply. We investigated changes in salinity, in conjunction with evaporation kinetics of treated wastewater by aquatic plants. These plants enhance the removal of pollutants by consuming them in the form of plant nutrients and through the microbial activity on their roots. In particular, this treatment applies to urban and agricultural sewage, where treatment units of different sizes can be applied at the pollution source while acting as green environments. In these treatment units, increased salinity due to effect of evapotranspiration (ET) must be managed. The rates of evaporation (E) from the free water surface and transpiration (T) from the plants were determined under field and laboratory conditions. To this end, batch experiments were performed with floating and emergent aquatic plants. After 4 days in the presence of floating plants, the biochemical oxygen demand (BOD) decreased from its 100-110 mg L(-1) initial value down to 30-40 mg L(-1) (65% to 70% removal), concurrent with a 2% to 5% increase in the chlorides level, and 5% to 8% in the electroconductivity. The ET rates were found to be a significant factor in the water balance governing the treatment process. The results of this work provide guidelines for recommended wastewater treatment times that safeguard against undesirable rises in salinity, yet with marginal change in parameters such as BOD. The change of salinity is shown to be relatively minor in the first days of treatment where the change in BOD is faster, whereas in the following days the picture is reversed. This result indicates the advantage of applying shorter treatment periods when the rise in salinity is avoided.

A tale of three acaropathogenic fungi in Israel: Hirsutella, Meira and Acaromyces.

We review published and unpublished studies conducted in Israel with six acaropathogenic fungi, assayed in order to control the citrus rust mite, Phyllocoptruta oleivora (Ashmead) (CRM). Hirsutella thompsonii Fisher was introduced twice, killed 80-90% of the exposed mites, but due to its requirements for near-saturation humidities was deemed unsuitable for local outdoors conditions. Hirsutella kirchneri (Rostrup) Minter et al. and Hirsutella necatrix Minter et al. were also introduced and assayed against CRM and spider mites, but their efficacy was unsatisfactory. Three indigenous fungi found to be associated with mites, Meira geulakonigii, Meira argovae and Acaromyces ingoldii--all three recently described by Boekhout, Gerson, Scorzetti & Sztejnberg--were assayed against several mites. Meira geulakonigii killed 80-90% of several spider mites and of the CRM, and caused some mortality of Iphiseius degenerans (Berlese), one out of three phytoseiid predators assayed. Mortality was not due to parasitization; extracts from the media in which the fungi had developed caused considerable mite death, suggesting that it was a result of fungal toxins. Data from a field study indicated that spraying blastoconidia of M. geulakonigii on grapefruits infested by CRM significantly reduced pest-incurred damage from 23 to 13%. Applying qRT-PCR methodology indicated that M. geulakonigii was endophytic within sealed grapefruit flowers and in the flavedo of the fruits' peel. Neither in the laboratory nor in the field was any evidence ever obtained that this fungus damaged the plants, leading us to hypothesize that M. geulakonigii serves as a "body guard" of grapefruits (and perhaps other plants as well). All three fungi suffered very little mortality after being exposed to various insecticides and acaricides that are in current local use (with the exception of sulfur). The ability of M. geulakonigii to reduce mite numbers without affecting the host plant, the minimal fungal effect on some predatory mites, its endophytic nature along with the apparent tolerance of M. geulakonigii to many insecticides and acaricides, suggest that this fungus could be suitable for integrated pest management (IPM) program.

Seniors at risk: the association between the six-month use of publicly funded home support services and quality of life and use of health services for older people.

This study examines the baseline characteristics and changes in health status and cost of use of health services associated with use of publicly funded home support services. The analysis includes 122 people 75 years of age or more who were eligible for home support services. Over a 6-month period, one third of the sample used home support services for more than 1 hr/week; these seniors had higher rates of depression and cognitive impairment, lower levels of physical and emotional functioning, and less effective coping styles than those who used fewer services. Cognitive impairment explained 17 per cent of the variation in use of home support services. At 6 months, use of home support services for more than 1 hr/week by seniors with higher levels of need was associated with lower cost of use of health services and lower levels of improvement in health status. These findings suggest the need for further research to identify efficacious ways of providing home support services to this population to enhance their health status using available resources.

The Control of Hypertension In Pregnancy Study pilot trial.

OBJECTIVE: To determine whether 'less tight' (versus 'tight') control of nonsevere hypertension results in a difference in diastolic blood pressure (dBP) between groups. DESIGN: Randomised controlled trial (ISRCTN#57277508). SETTING: Seventeen obstetric centres in Canada, Australia, New Zealand, and UK. POPULATION: Inclusion: pregnant women, dBP 90-109 mmHg, pre-existing/gestational hypertension; live fetus(es); and 20-33(+6) weeks. Exclusion: systolic blood pressure > or = 170 mmHg and proteinuria, contraindication, or major fetal anomaly. METHODS: Randomisation to less tight (target dBP, 100 mmHg) or tight (target dBP, 85 mmHg) blood pressure control. MAIN OUTCOME MEASURES: Primary: mean dBP at 28, 32 and 36 weeks. Secondary: clinician compliance and women's satisfaction. Other: serious perinatal and maternal complications. RESULTS: A total of 132 women were randomised to less tight (n = 66; seven had no study visit) or tight control (n= 66; one was lost to follow up; seven had no study visit). Mean dBP was significantly lower with tight control: -3.5 mmHg, 95% credible interval (-6.4, -0.6). Clinician compliance was 79% in both groups. Women were satisfied with their care. With less tight (versus tight) control, the rates of other treatments and outcomes were the following: post-randomisation antenatal antihypertensive medication use: 46 (69.7%) versus 58 (89.2%), severe hypertension: 38 (57.6%) versus 26 (40.0%), proteinuria: 16 (24.2%) versus 20 (30.8%), serious maternal complications: 3 (4.6%) versus 2 (3.1%), preterm birth: 24 (36.4%) versus 26 (40.0%), birthweight: 2675 +/- 858 versus 2501 +/- 855 g, neonatal intensive care unit (NICU) admission: 15 (22.7%) versus 22 (34.4%), and serious perinatal complications: 9 (13.6%) versus 14 (21.5%). CONCLUSION: The CHIPS pilot trial confirms the feasibility and importance of a large definitive trial to determine the effects of less tight control on serious perinatal and maternal complications.

Women's views of their experiences in the CHIPS (Control of Hypertension in Pregnancy Study) Pilot Trial.

BACKGROUND: Satisfaction with maternity care is strongly related to the patient-caregiver relationship and involvement in the decision-making process. We sought to compare women's views about their care in a randomized trial of 'less tight' vs. 'tight' control of non-proteinuric pre-existing or gestational hypertension in pregnancy. METHODS: In the CHIPS Pilot Trial, women completed a postpartum questionnaire to assess their likes and dislikes about their blood pressure (BP) management and trial participation. Comparisons were descriptive. RESULTS: Baseline information was similar for the 'less tight' and 'tight' control groups. Of 132 women, 126 (95.5%) from 17 centers completed a postpartum questionnaire, usually within days of delivery. At least 90% of women in both groups were satisfied with their care, and would be willing to participate again or recommend participation to a friend. Women in both the 'less tight' and 'tight' groups were satisfied with BP management (98.4% vs. 95.1%), and the frequency of tests of maternal and fetal well being. Half of women in both groups perceived that their BP was too high and that caregivers thought that their BP was too high. More women in the 'less tight' (vs. the 'tight') control group took less medication than expected (71.7% vs. 38.2%). More women in the 'tight' (vs. the 'less tight') group took more medication than they expected (60.0% vs. 22.2%). At least 60% of all women used home BP monitoring. CONCLUSION: In the CHIPS Pilot Trial, while women stated that they were satisfied with their BP management and care, a surprising 50% in both groups thought that their BP was too high. The majority of women used home BP monitoring, the role of which must be further defined in hypertensive pregnancies.

Molecular origin of the aging effects in glyceraldehyde-3-phosphate dehydrogenase.

Rat muscle glyceraldehyde-3-phosphate dehydrogenase was reacted with two reagents aimed at the highly reactive cysteine-149 residue in the active site of the enzyme. The enzyme was rapidly inactivated by iodine monochloride. Complete inactivation occurred when approx. 6 mol ICl were added per mol enzyme, indicating that reactions which compete with the reagent's interaction with cysteine-149 take place. Iodine was also found to inactivate the enzyme rapidly and effectively, and, when not in excess, this reagent interacted specifically with cysteine-149. The fraction of original enzymatic activity which could be restored by 2-mercaptoethanol in enzyme samples inhibited by 4.2 mol I2/mol enzyme, decreased with time to a limiting value of 0.6 reached after approx. 15 min. The enzyme thus treated showed a remarkable similarity to enzyme samples purified from old rats, both in its activity and in NAD+ binding patterns under various conditions. It is concluded that the structural modifications induced in the modified enzyme resemble the age-related modifications in native 'old' enzyme. These results demonstrate that the origin of the age-related effects in glyceraldehyde-3-phosphate dehydrogenase is in subtle, post-synthetic structural changes. The inactivation reactions described above require a non-reducing environment for the enzyme. Whether such conditions do exist in cells of old animals is the subject of future studies.

Age-related modifications in rat cardiac phosphoglycerate kinase. Rejuvenation of the old enzyme by unfolding-refolding.

The occurrence of age-related modifications in functional and structural properties of several enzymes has been documented; however, the molecular basis of this phenomenon is still mostly unexplained. In the present work a comparative study of phosphoglycerate kinase preparations isolated from hearts of young and old rats was undertaken. Marked age-related effects were revealed in the heat-inactivation kinetics of the enzyme, similar to the ones previously found in purified muscle phosphoglycerate kinase. In view of the previously reported failure of immunotitration to distinguish between phosphoglycerate kinase forms in crude heart extracts from young and old rats, it appears likely that the modifications in old rat heart phosphoglycerate kinase are in a domain which is not involved in antibody binding, and may be localized in the interior of the enzyme. These age-related modifications were completely relieved by extensive unfolding of the enzyme in 2 M guanidine hydrochloride, followed by enzyme reactivation upon dilution of the denaturant. The refolding products of young and old enzymes displayed identical heat-inactivation kinetics as native young phosphoglycerate kinase. It is concluded that the age-related alterations in rat cardiac phosphoglycerate kinase, like those found in the muscle enzyme, are purely conformational and hence develop postsynthetically.

The interaction of liver alcohol dehydrogenase with NADH as studied by differential protein denaturation.

Heat denaturation of horse liver alcohol dehydrogenase was followed in the presence of isobutyramide at various degrees of saturation of the binding sites by NADH. A study of the fluorescence enhancement which is observed when an excess of NADH is added to the partially denatured mixtures provides information regarding the relative concentrations of mono- and bioccupied enzyme molecules. This approach is of value in situations when the association constants for coenzyme are so large that the concentration of the free ligand is negligible. The results obtained indicate that the binding of NADH to liver alcohol dehydrogenase follows the statistically predicted distribution. At the same time evidence was obtained for interaction between the two subunits of the enzyme.

Denaturation of glucose-6-phosphate dehydrogenase from Leuconostoc mesenteroides by guanidine hydrochloride; identification of inactive, partially unfolded, dimeric intermediates.

The denaturation of the dimeric enzyme glucose-6-phosphate dehydrogenase from Leuconostoc mesenteroides by guanidine hydrochloride has been studied using enzymatic activity, intrinsic fluorescence, circular dichroism, and light scattering measurements. Equilibrium experiments at 25 degrees C revealed that between 0.9 and 1.2 M denaturant the enzyme underwent a conformational change, exposing tryptophan residues to solvent, with some loss of secondary structure and a complete loss of enzymatic activity but without dimer dissociation to subunits. This inactive, partially unfolded, dimeric intermediate was susceptible to slow aggregation, perhaps due to exposure of 'sticky' hydrophobic stretches of the polypeptide chain. A second equilibrium transition, reflecting extensive unfolding and dimer dissociation, occurred only at denaturant concentrations above 1.4 M. Kinetics experiments demonstrated that in the denaturant concentration range of 1.7-1.9 M the fluorescence change occurred in two distinct steps. The first step involved a large, very rapid drop in fluorescence whose rate was strongly dependent on the denaturant concentration. This was followed by a small, relatively slow rise in the emission intensity, the rate of which was independent of denaturant concentration. Enzymatic activity was lost with a denaturant-concentration-dependent rate, which was approx. 3-times slower than the rate of the first step in fluorescence change. A denaturation mechanism incorporating several unfolding intermediates and which accounts for all the above results is presented and discussed. While the fully unfolded enzyme regained up to 55% of its original activity upon dilution of denaturant to a concentration that would be expected to support native enzyme, denaturation intermediates were able to reactivate only minimally and in fact were found to aggregate and precipitate out of solution.

Renaturation of glucose-6-phosphate dehydrogenase from Leuconostoc mesenteroides after denaturation in 4 M guanidine hydrochloride: kinetics of aggregation and reactivation.

In 4 M guanidine hydrochloride (GdnHCl), the dimeric enzyme glucose-6-phosphate dehydrogenase from Leuconostoc mesenteroides (G6PD) dissociated to subunits and was extensively unfolded. Rapid dilution of this high GdnHCl concentration allowed G6PD to partially renature, as measured by enzyme reactivation, to a level which depended on the conditions employed. The fraction of the enzyme which did not renature aggregated and precipitated out of solution, a process which could not be substantially prevented by stabilizing additives. Based on the enzyme concentration dependence of the reactivation yield and on a comparison of the aggregation and reactivation rates, it was determined that aggregation and reactivation compete kinetically for a partially-folded intermediate only very early in the process, during the rapid GdnHCl-dilution step. The kinetics of G6PD reactivation were sigmoidal, indicating that this process involves more than one rate-limiting reaction. The kinetics depended on enzyme concentration in a higher than first-order manner, indicating that association of subunits is one of the rate-limiting reactions. A renaturation mechanism compatible with these observations is described, which involves a bi-unimolecular (subunit association-folding) reaction sequence, with rate constants equal to 2.19 microM-1 min-1 and 0.140 min-1, respectively. This mechanism involves an inactive, dimeric, G6PD-folding intermediate, a species whose existence has recently been established by equilibrium denaturation experiments (Plomer, J.J. and Gafni, A. (1992) Biochim. Biophys. Acta 1122, 234-242).

Aggregation of an amyloidogenic fragment of human islet amyloid polypeptide.

Native human islet amyloid polypeptide (hIAPP) has been identified as the major component of amyloid plaques found in the pancreatic islets of Langerhans of persons affected by type 2 diabetes mellitus. Early studies of hIAPP determined that a segment of the molecule, amino acids 20-29, is responsible for its aggregation into amyloid fibrils. The present study demonstrates that the aggregation of hIAPP 20-29-Trp is a nucleation-dependent process, displaying a distinct lag time before the onset of rapid aggregation. Moreover, the lag time can be eliminated by seeding the sample of unaggregated peptide with preformed fibrils. In contrast to the expectation from the conventional model of nucleation-dependent aggregation, however, the lag time of hIAPP aggregation does not depend on peptide concentration. To explain this observation, a modified version of the standard model of nucleation-dependent aggregation is presented in which the monomeric peptide concentration is buffered by an off-aggregation-pathway formation of peptide micelles.

Circular polarization of fluorescence of chlorophyll in solution and in native structures.

Chlorophyll dimers in solution, subchlorplast particles and chloroplasts were investigated by their circular dichroism and circular polarization of their fluorescence, which reflect their optical rotatory power in the ground state and electronically excited state, respectively. The chlorophyll dimers in fluid solution lose their optical activity upon electronic excitation, reflecting a marked concomitant change in the structure of the dimers. This change is arrested in a solution of very high viscosity. The pronounced difference between the circular polarization of the dimers in fluid media and that of subchloroplast particles and chloroplasts indicates that the former are not suitable models for associated chlorophyll in native structures in electronically excited states. Impairment of the photochemical activity of chloroplasts by heat treatment is accompanied by a reduction of the circular polarization of the fluorescence, which probably reflects a disorganization in structure. The same extent of circular polarization was observed in the fluorescence of chloroplasts regardless whether the reaction centers are open or closed; thus either the same molecules are emitting in the two cases or, if different molecules emit, they are packed in a similar way.