Abordagem cutânea na necrólise epidérmica tóxica / Cutaneous approach in toxic epidermal necrolysis

Introdução: Necrólise epidérmica tóxica é uma erupção mucocutânea aguda grave, geralmente induzida por medicamentos, associada a alta taxa de morbidade e mortalidade. Os cuidados com as lesões mucosas e cutâneas e a abordagem multidisciplinar são muito importantes para o prognóstico e sequelas futuras. Objetivos: Discutir os principais aspectos dessa síndrome por meio da revisão de literatura, ilustrada por um caso clínico. Métodos: Revisão de literatura utilizando bases de dados on-line PubMed e Scielo. Incluímos artigos em língua inglesa, portuguesa, francesa e espanhola, e ilustração com caso clínico pediátrico. Termos procurados foram "toxic epidermal necrolysis", "Stevens-Johnson overlap", ''necrólise epidérmica tóxica'', ''síndrome Stevens-Johnson''. Resultados: Apresentamos dados para guiar o manejo de pacientes com necrólise epidérmica tóxica para cirurgiões plásticos, pediatras, intensivistas, dermatologistas e emergencistas. O caso tratado teve evolução favorável, sem sequelas cutâneas. Conclusão: O alto nível de suspeição é imprescindível para um diagnóstico e estratificação de risco adequados e instituição precoce de medidas de suporte, e o tratamento deve ser realizado por uma equipe multidisciplinar treinada para reduzir sequelas e mortalidade.

Introduction: Toxic epidermal necrolysis is a severe acute mucocutaneous condition usually induced by drugs associated with a high rate of morbidity and mortality. The care of the mucous lesions and skin and a multidisciplinary approach are very important for the prognosis and future sequelae. Objectives: To discuss the main aspects of this syndrome through a literature review illustrated by a clinical case. Methods: Review of the literature using the PubMed and SciELO online databases was performed. Articles in English, Portuguese, French, and Spanish were included and illustrated with a pediatric clinical case. The keywords used were as follows: "toxic epidermal necrolysis," "Stevens-Johnson overlap," "necrólise epidérmica tóxica," and "síndrome Stevens-Johnson." Results: We presented data to guide the management of patients with toxic epidermal necrolysis for plastic surgeons, pediatricians, intensivists, dermatologists, and emergency physicians. The case treated had a favorable disease course without sequelae. Conclusion: A high level of suspicion is necessary for an adequate diagnosis and risk stratification, and early support measures and treatment should be performed by a multidisciplinary team trained to minimize damage and mortality.

Computer-assisted sperm analysis parameters in young fertile sperm donors and relationship with age.

Sperm parameter values have been shown to decline with age, according to conventional sperm analysis. However, the effect of age on sperm kinematic parameters has been rarely studied, especially in young fertile men. Here, we studied Computer-Assisted Sperm Analysis (CASA) parameters in a large cohort of men with proven fertility, in order to determine if there is a decline with age in this young fertile population. This retrospective analysis of CASA parameters was conducted on all donors included in the sperm donor programme in the Assisted Reproductive Techniques (ART) Centre of the University Hospital of Nantes between 2006 and 2009. Sperm concentration, motility, and kinetic parameters were recorded by a HTM-Ceros system and compared in 3 groups of sperm donors according to their age: <35 years, 36-40 years, and 41-44 years. A total of 362 ejaculates from 138 donors were analyzed. Values for ALH, VCL, LIN, and STR significantly decreased with age. Sperm concentration, motile sperm proportion, and other kinetic parameters did not differ significantly among the groups. The use of CASA allowed the identification of ALH, VCL, LIN, and STR age-related decrease in young men with proven fertility.

Ovarian reserve and in vitro fertilization cycles outcome according to women smoking status and stimulation regimen.

PURPOSE: Smoking is known to be deleterious on female fertility and in vitro fertilization (IVF) outcome, probably partly through ovarian reserve alteration. Recently, anti-Müllerian hormone (AMH) and antral follicle count (AFC) have been shown to be the most accurate ovarian reserve markers. Here, we compared ovarian reserve markers in women undergoing IVF according to smoking status and stimulation regimen. METHODS: AFC, AMH, basal FSH, LH and estradiol, and IVF outcome were compared in 277 women undergoing IVF. Smoking status and ovarian stimulation protocol (i.e. agonists or antagonists) were recorded. RESULTS: Active smoking women had lower AMH and modified follicles' size repartition in AFC compared to non-smokers. They also experienced poorer IVF outcome with decreased ovarian response and lower pregnancy rate. This remained true in both antagonist and agonist stimulation protocol groups. CONCLUSION: Active smoking in infertile women is associated with ovarian reserve alteration, as reflected by AFC modification and decreased serum AMH, and leads to poor prognosis in ART cycles, whatever the stimulation protocol used. Infertile women should be strongly discouraged from smoking before they start IVF cycles.

Sperm banking and assisted reproductive outcome in men with cancer: a 10 years' experience.

BACKGROUND: As cancer therapy can be harmful to spermatogenesis, men are generally advised to cryopreserve sperm before gonadotoxic treatment. Here, we compared fresh and frozen-thawed sperm quality in patients according to cancer type, and reported use rate in subsequent assisted reproductive technology (ART) cycles. METHODS: This retrospective analysis of a sperm cryopreservation program in all men suffering from cancer was conducted at the University Hospital of Nantes between 1997 and 2007. RESULTS: A total of 1042 men were referred for sperm cryopreservation during this period (438 testicular cancer, 184 other solid cancers, 278 lymphoma and 142 other haematological malignancies). A total of 2577 ejaculates from 1009 men were studied. Sperm characteristics and sperm sensitivity to the freezing process varied according to the cancer type. Frozen sperm was used in 82 patients, with 112 in vitro fertilization and 66 intrauterine insemination cycles performed, leading to a clinical pregnancy rate per cycle of 23.2 and 12%, respectively. CONCLUSION: Sperm quality and motility alteration during the freezing process can differ according to the type of cancer, but sperm frozen before gonadotoxic treatment in cancer patients can be successfully used in ART.

Prolonging GnRH-agonist to achieve ovarian suppression does not compromise the results of a long protocol.

OBJECTIVES: In the long gonadotropin-releasing hormone agonist (GnRHa) protocols, stimulation is delayed until complete pituitary-ovarian suppression has been achieved, which usually takes a minimum of 10 days. In women who do not achieve timely suppression we set out to evaluate if prolonging GnRHa affects the results of the IVF process. STUDY DESIGN: We analyzed cycle and pregnancy outcome in 506 consecutive women undergoing IVF-ET after a standardized long GnRHa protocol, according to the time required to achieve ovarian suppression (i.e. estradiol< 40 pg/mL and no follicle >6mm at ultrasound). RESULTS: Suppression was obtained after 14 GnRHa days in 383 (75.70%) women (Group 1) and 123 (24.30%) women (Group 2) required a mean ± SD (range) of 10 ± 4 (7-28) additional days to achieve complete suppression. Both groups were comparable for baseline clinical and biological characteristics. The rate of cancelled cycles due to poor ovarian response, the number of the oocytes retrieved, fertilization rates, the number and quality of the embryos cultured and transferred were similar in both groups, as well as the pregnancy, implantation and live birth rates. In Group 2, receiver-operator characteristics analysis showed that the probability of pregnancy was not related to the duration of GnRHa treatment. CONCLUSIONS: In a standardized long GnRHa protocol, prolonging desensitization to achieve complete ovarian suppression does not affect the outcome.

Predictive factors of healthy term birth after single blastocyst transfer.

BACKGROUND: Blastocyst culture and elective single embryo transfer programmes are increasingly used to reduce multiple pregnancies after IVF. To optimize the results, there is a need to better select embryos, to implement efficient cryopreservation programmes and to refine selection criteria. In the present study, we set out to identify relevant clinical predictors of healthy term birth (HTB) after single blastocyst transfer (SBT). DESIGN: analysis of prospectively collected database. SETTING: University IVF centre in Nantes, France. In 872 infertile women undergoing their first IVF cycle with SBT between January 2007 and December 2008, multivariable analysis and logistic regression were used to identify predictive factors of HTB, i.e. delivery of a live born term singleton of ≥ 2500 g, surviving at least 28 days with no reported congenital anomaly. RESULTS: Of 304 deliveries, there were 16 twin pairs (5.5%) and no high order deliveries. The rate of HTB was 266/872 (30.5%). Univariate analysis showed that the probability of HTB was significantly higher in women under 35 years [odds ratio (OR):1.75, 0.95 confidence interval (CI): 1.2-2.5, P = 0.001], in women with a BMI < 30 kg/m² (OR: 3.0, 0.95 CI: 1.5-5.9, P = 0.001), in non-smoking women (OR: 2.2, 0.95 CI: 1.5-3.2, P < 0.0001), and after Day 5 compared with after Day 6 transfer (OR: 2.65, 0.95 CI: 1.8-3.8, P < 0.0001). Multivariable analysis showed that BMI, smoking and day of embryo transfer were independent predictors of HTB, regardless of female age. CONCLUSIONS: After SBT, female obesity and smoking reduce the chance of HTB, independent of female age. Day 6 transfer should be avoided.

Smoking among French infertility specialists: habits, opinions and patients' management.

OBJECTIVE: The deleterious effects of tobacco on fertility are now largely demonstrated. Little is known, however, about how infertility doctors communicate on smoking and about their own smoking habits. In this study, we examined smoking habits among French infertility specialists and their attitudes towards infertile couples' exposure to tobacco. STUDY DESIGN: A postal survey was sent in 2009 to the 803 French certified physicians (gynaecologists, urologists, endocrinologists and embryologists) specializing in infertility. Demographical data, smoking habits and attitude towards patients' smoking were recorded. Statistical analysis and multiple correspondence analysis were performed in order to identify differences among physicians according to age, gender, occupation or smoking status. RESULTS: Response rate was 42.3%. Half of the respondents were male, 41% were under 45 years, 37% were embryologists and 53.3% were gynaecologists. Thirteen percent reported current smoking. More than 80% always asked their patients about smoking status and cannabis consumption. Most physicians specifically informed infertile couples on tobacco, advised them to quit and proposed smoking cessation therapies. Only 24% refused care unless smoking cessation occurred. Statistical analysis showed some differences among subgroups according to gender, occupation or age. Surprisingly, results were comparable according to smoking status. CONCLUSION: Most infertility specialists are aware of the deleterious effects of tobacco on fertility and ask their patients to quit. The heterogeneity in infertile patients' management, however, underlines the need for better professional and patients' information on smoking.

Monozygotic triplet pregnancies after single blastocyst transfer: two cases and literature review.

Following IVF, single blastocyst transfer has been thought to reduce the risks of high-order multiple pregnancies. This is a report of two cases of monozygotic triplet pregnancies after single blastocyst transfer and a review of the current concepts of the pathogenesis of multiple monozygotic pregnancies as well as the options for managing these high-risk pregnancies. Both cases were reduced to a twin pregnancy by selective cord coagulation at 15-16 weeks. Whereas one patient had uneventful pregnancy until labour was induced for growth arrest and cord Doppler abnormalities in one twin, the other developed a severe twin-to-twin transfusion syndrome which required fetoscopic laser surgery at 21 weeks. In both cases, healthy twins were delivered by Caesarean section at 34.5 and 34 weeks, respectively. As the predictors of their occurrence are not fully understood, patients should be informed of the risks of monozygotic pregnancies after single blastocyst transfer.

IVF conversion to IUI in poor responders: an observational study.

PURPOSE: The purpose of this study was to evaluate the significance of converting an IVF stimulation cycle with poor ovarian response to an IUI cycle. METHODS: Between January and December 2007, 47 cycles of IVF conversion to IUI were retrospectively studied in 44 infertile women who had a low response to ovarian hyperstimulation for IVF. Patients' characteristics, ovarian stimulation, and ovarian response and outcome were collected and compared with those of 41 women undergoing ovum pickup for IVF with poor ovarian response (n = 44 cycles) in the same period. RESULTS: Women in the conversion group had slightly lower ovarian reserve, shorter stimulation with higher rFSH doses, lower peak estradiol and fewer mature follicles than in the IVF group. Pregnancy rates were comparable in both groups, though clinical pregnancy rate tended to be higher in the conversion group than in the IVF group. CONCLUSIONS: Thus, pregnancy rate in the conversion group compares favourably with IVF outcome in such circumstances. This means that IVF conversion to IUI in poor responders who are suitable for IUI is a valuable alternative that should be considered in their management.

Predictive value of ovarian reserve markers in smoking and non-smoking women undergoing IVF.

Ovarian reserve markers are now widely used in IVF centres in order to predict ovarian response and adapt ovarian stimulation protocols. In this study, the respective performance of day-3 FSH, oestradiol and anti-Müllerian hormone concentrations and antral follicle count for the prediction of poor ovarian response to ovarian stimulation and pregnancy in IVF cycles were compared in women according to their smoking status. The analysis of 384 IVF cycles showed that anti-Müllerian hormone concentration and antral follicle count were the best predictors of poor ovarian response and performed better in non-smokers than in smokers, for which no parameter could predict pregnancy.

Computer-Assisted Sperm Analysis (CASA) parameters and their evolution during preparation as predictors of pregnancy in intrauterine insemination with frozen-thawed donor semen cycles.

OBJECTIVE: To study the potential of CASA parameters in frozen-thawed donor semen before and after preparation on silica gradient as predictors of pregnancy in IUI with donor semen cycles. STUDY DESIGN: CASA parameters were measured in thawed donor semen before and after preparation on a silica gradient in 132 couples undergoing 168 IUI cycles with donor semen. The evolution of these parameters throughout this process was calculated. The relationship with cycle outcome was then studied. RESULTS: Clinical pregnancy rate was 18.4% per cycle. CASA parameters on donor semen before or after preparation were not significantly different between pregnancy and failure groups. However, amplitude of lateral head displacement (ALH) of spermatozoa improved in all cycles where pregnancy occurred, thus predicting pregnancy with a sensitivity of 100% and a specificity of 20%. CONCLUSIONS: Even if CASA parameters do not seem to predict pregnancy in IUI with donor semen cycles, their evolution during the preparation process should be evaluated, especially for ALH. However, the link between ALH improvement during preparation process and pregnancy remains to be explored.

How soon can I be proficient in embryo transfer? Lessons from the cumulative summation test for learning curve (LC-CUSUM).

BACKGROUND: Embryo transfer, a crucial step for achieving pregnancy after in vitro fertilization, is an operator-dependent technique but the number of procedures required for a trainee to reach proficiency is unknown. We set out to evaluate the learning curve (LC) of embryo transfer using a specifically designed statistical tool. METHODS: The first embryo transfers performed by five trainees were monitored by the cumulative summation test for learning curve (LC-CUSUM), a statistical tool designed to indicate when a process has reached a predefined level of performance. The main outcome measure was a positive hCG test. A 40% pregnancy rate (PR) per transfer was chosen to define adequate performance and a PR of 20% was considered inadequate. After the learning phase, standard CUSUM were implemented to ensure that performance was maintained. The same CUSUM parameters were also applied to monitor 241 consecutive embryo transfers performed by a senior gynaecologist. RESULTS: Between 11 and 99 embryo transfers were necessary for the trainees to reach the predefined level of performance. Simple and intuitive graphical representations of the LCs were generated. CUSUM tests confirmed that performance was maintained after the learning phase. The PR of the senior gynaecologist was 42.7% and the CUSUM showed that performance remained adequate throughout the 241 procedures. CONCLUSIONS: This study provides an exportable model for a quantitative monitoring of the LC of embryo transfer as well as a reference curve for continuous monitoring of performance in embryo transfer. The length of the LC of embryo transfer is highly variable, justifying a tailored training to learn this procedure.

A cycle-based model to predict blastocyst transfer cancellation.

BACKGROUND: Extended culture for blastocyst transfer is thought to result in embryos with high implantation potential, enabling the transfer of fewer embryos and the reduction of multiple pregnancies after in vitro fertilization (IVF). However, one major drawback of extended culture is the risk of transfer cancellation if no blastocyst develops by Day 5, despite the observation of adequate early embryo development. We set out to develop a model to predict blastocyst transfer cancellation. METHODS: The model was built from 562 consecutive first IVF cycles and tested on an independent validation cohort. Multivariable logistic regression analysis was used to test the association of patient and cycle characteristics with the presence of cultured blastocysts on Day 5 and to create a nomogram. The model's performance was quantified by discrimination and calibration and clinical utility was evaluated for various thresholds. RESULTS: Fertilization technique, number and quality ratio of the Day 3 embryos and female age were independently associated with blastocyst development. The final prediction model showed an area under the curve (AUC) of 0.75 in the training set (95% confidence interval (CI): 0.73-0.77) and was well calibrated. The AUC for the validation data set was 0.80 (95% CI: 0.78-0.83) and calibration was acceptable. Using a decision threshold of 0.55, the model showed a negative predictive value of 80.5% and a false positive rate of 17%. CONCLUSION: A cycle-based model could prove clinically-relevant for reducing the incidence of cancelled Day 5 transfers.

Charge stabilization and entropy reduction of central lysine residues in fructose-bisphosphate aldolase.

Fructose-1,6-bisphosphate muscle aldolase is an essential glycolytic enzyme that catalyzes reversible carbon-carbon bond formation by cleaving fructose 1,6-bisphosphate to yield dihydroxyacetone phosphate (DHAP) and d-glyceraldehyde phosphate. To elucidate the mechanistic role of conserved amino acid Asp-33, Asn-33 and Ser-33 mutants were examined by kinetic and structural analyses. The mutations significantly compromised enzymatic activity and carbanion oxidation in presence of DHAP. Detailed structural analysis demonstrated that, like native crystals, Asp-33 mutant crystals, soaked in DHAP solutions, trapped Schiff base-derived intermediates covalently attached to Lys-229. The mutant structures, however, exhibited an abridged conformational change with the helical region (34-65) flanking the active site as well as pK(a) reductions and increased side chain disorder by central lysine residues, Lys-107 and Lys-146. These changes directly affect their interaction with the C-terminal Tyr-363, consistent with the absence of active site binding by the C-terminal region in the presence of phosphate. Lys-146 pK(a) reduction and side chain disorder would further compromise charge stabilization during C-C bond cleavage and proton transfer during enamine formation. These mechanistic impediments explain diminished catalytic activity and a reduced level of carbanion oxidation and are consistent with rate-determining proton transfer observed in the Asn-33 mutant. Asp-33 reduces the entropic cost and augments the enthalpic gain during catalysis by rigidifying Lys-107 and Lys-146, stabilizing their protonated forms, and promoting a conformational change triggered by substrate or obligate product binding, which lower kinetic barriers in C-C bond cleavage and Schiff base-enamine interconversion.

Predictive value of CASA parameters in IUI with frozen donor sperm.

The objective of this study was to determine if characteristics of sperm motion determined by computer-aided semen analysis (CASA) after thawing and preparation on discontinuous gradient could predict pregnancy outcome after intrauterine insemination (IUI) from frozen donor sperm. A retrospective analysis of 100 non-selected women undergoing 171 consecutive donor insemination cycles was conducted between January 2006 and April 2007. Semen samples from all donors were analysed after thawing and density gradient preparation. Women who became pregnant and those who did not were comparable in terms of age, ovarian stimulation regimen and indication of IUI with donor semen. Pregnancy rate per cycle was 21.8%, and pregnancy occurred after 2.5 IUI cycles on average. Motility parameters of sperm measured by CASA (VAP, VCL, VSL, LIN, STR, and ALH) and total spermatozoa concentration after preparation on discontinuous gradient showed no difference in both groups. Progressive and total motile spermatozoa concentration, as well as progressive and total motile percentages was significantly higher in pregnancy group. The receiver operating characteristic (ROC) curve analysis showed that total motile percentage >17% and motile concentration >0.9 x 10(6)/mL best predicted pregnancy. In a multivariate analysis, only total motility percentage was able to predict pregnancy. Sperm motility parameters of frozen-thawed prepared donor sperm obtained by CASA do not seem to predict pregnancy in IUI cycles. Total motile and progressive percentages and concentrations remain the best prognostic elements for pregnancy in IUI with donor semen.

Active smoking compromises IVF outcome and affects ovarian reserve.

Although the association between smoking and female infertility is now largely demonstrated, the proportion of smokers in women of reproductive age remains important. Tobacco contains numerous toxicants that could affect ovarian reserve and lead to poor prognosis in assisted reproductive techniques. To investigate the effect of female active smoking on ovarian reserve and IVF outcome, smoking status, hormonal status, i.e. serum FSH, oestradiol and anti-Müllerian hormone (AMH), ovarian response to hyperstimulation, i.e. mature oocytes retrieved, and IVF outcome, i.e. clinical pregnancy, were retrospectively analysed in 111 women undergoing IVF-embryo transfer cycles. Compared with non-smokers (n = 71), active smoking women (n = 40) had decreased ovarian response (12.12 +/- 5 versus 8.62 +/- 4 mature oocytes retrieved) to hyperstimulation and lower clinical pregnancy rate (29.6 versus 10.0%). Serum AMH concentrations were lower in the smoker group (3.86 +/- 1.92 versus 3.06 +/- 1.68 mug/l) and had no predictive value for ovarian response, inversely to non-smokers. In conclusion, active smoking is associated with poor prognosis in assisted reproduction cycles, i.e. ovarian response and pregnancy, and leads to altered ovarian reserve, as reflected by decreased serum AMH concentrations.

Stereospecific proton transfer by a mobile catalyst in mammalian fructose-1,6-bisphosphate aldolase.

Class I fructose-1,6-bisphosphate aldolases catalyze the interconversion between the enamine and iminium covalent enzymatic intermediates by stereospecific exchange of the pro(S) proton of the dihydroxyacetone-phosphate C3 carbon, an obligatory reaction step during substrate cleavage. To investigate the mechanism of stereospecific proton exchange, high resolution crystal structures of native and a mutant Lys(146) --> Met aldolase were solved in complex with dihydroxyacetone phosphate. The structural analysis revealed trapping of the enamine intermediate at Lys(229) in native aldolase. Mutation of conserved active site residue Lys(146) to Met drastically decreased activity and enabled trapping of the putative iminium intermediate in the crystal structure showing active site attachment by C-terminal residues 360-363. Attachment positions the conserved C-terminal Tyr(363) hydroxyl within 2.9A of the C3 carbon in the iminium in an orientation consistent with incipient re face proton transfer. We propose a catalytic mechanism by which the mobile C-terminal Tyr(363) is activated by the iminium phosphate via a structurally conserved water molecule to yield a transient phenate, whose developing negative charge is stabilized by a Lys(146) positive charge, and which abstracts the C3 pro(S) proton forming the enamine. An identical C-terminal binding mode observed in the presence of phosphate in the native structure corroborates Tyr(363) interaction with Lys(146) and is consistent with transient C terminus binding in the enamine. The absence of charge stabilization and of a mobile C-terminal catalyst explains the extraordinary stability of enamine intermediates in transaldolases.

A hydrophobic pocket in the active site of glycolytic aldolase mediates interactions with Wiskott-Aldrich syndrome protein.

Aldolase plays essential catalytic roles in glycolysis and gluconeogenesis. However, aldolase is a highly abundant protein that is remarkably promiscuous in its interactions with other cellular proteins. In particular, aldolase binds to highly acidic amino acid sequences, including the C terminus of the Wiskott-Aldrich syndrome protein, an actin nucleation-promoting factor. Here we report the crystal structure of tetrameric rabbit muscle aldolase in complex with a C-terminal peptide of Wiskott-Aldrich syndrome protein. Aldolase recognizes a short, four-residue DEWD motif (residues 498-501), which adopts a loose hairpin turn that folds around the central aromatic residue, enabling its tryptophan side chain to fit into a hydrophobic pocket in the active site of aldolase. The flanking acidic residues in this binding motif provide further interactions with conserved aldolase active site residues Arg-42 and Arg-303, aligning their side chains and forming the sides of the hydrophobic pocket. The binding of Wiskott-Aldrich syndrome protein to aldolase precludes intramolecular interactions of its C terminus with its active site and is competitive with substrate as well as with binding by actin and cortactin. Finally, based on this structure, a novel naphthol phosphate-based inhibitor of aldolase was identified, and its structure in complex with aldolase demonstrated mimicry of the Wiskott-Aldrich syndrome protein-aldolase interaction. The data support a model whereby aldolase exists in distinct forms that regulate glycolysis or actin dynamics.

High resolution reaction intermediates of rabbit muscle fructose-1,6-bisphosphate aldolase: substrate cleavage and induced fit.

Crystal structures were determined to 1.8 A resolution of the glycolytic enzyme fructose-1,6-bis(phosphate) aldolase trapped in complex with its substrate and a competitive inhibitor, mannitol-1,6-bis(phosphate). The enzyme substrate complex corresponded to the postulated Schiff base intermediate and has reaction geometry consistent with incipient C3-C4 bond cleavage catalyzed Glu-187, which is adjacent by to the Schiff base forming Lys-229. Atom arrangement about the cleaved bond in the reaction intermediate mimics a pericyclic transition state occurring in nonenzymatic aldol condensations. Lys-146 hydrogen-bonds the substrate C4 hydroxyl and assists substrate cleavage by stabilizing the developing negative charge on the C4 hydroxyl during proton abstraction. Mannitol-1,6-bis(phosphate) forms a noncovalent complex in the active site whose binding geometry mimics the covalent carbinolamine precursor. Glu-187 hydrogen-bonds the C2 hydroxyl of the inhibitor in the enzyme complex, substantiating a proton transfer role by Glu-187 in catalyzing the conversion of the carbinolamine intermediate to Schiff base. Modeling of the acyclic substrate configuration into the active site shows Glu-187, in acid form, hydrogen-bonding both substrate C2 carbonyl and C4 hydroxyl, thereby aligning the substrate ketose for nucleophilic attack by Lys-229. The multifunctional role of Glu-187 epitomizes a canonical mechanistic feature conserved in Schiff base-forming aldolases catalyzing carbohydrate metabolism. Trapping of tagatose-1,6-bis(phosphate), a diastereoisomer of fructose 1,6-bis(phosphate), displayed stereospecific discrimination and reduced ketohexose binding specificity. Each ligand induces homologous conformational changes in two adjacent alpha-helical regions that promote phosphate binding in the active site.

[Role of Fallopian tube in fertilization]. / Rôle de la trompe dans la fécondation.

Fallopian tubes are complex organ where fertilization occurs after inverse migration of spermatozoa and oocyte. However, tube cannot be restricted to be fertilization site. The different tubal segments represent specific microenvironments to favour capacitation and fertilization process and to support early embryonic development. Tubal physiology permits tubal transport of gametes and embryon on adequate time by variations of smooth muscles contractility among tubal segments and during menstrual cycle. Tubes should control the number of competent spermatozoa present on fertilization site. Composition and viscosity of tubal fluid also vary along the tube and during cycle. Specific components of tubal fluid such as HuOGP interfere with gamete maturation, fertilization process and early embryonic development. Alteration of part of these functions could explain some tubal infertilities leading with normal tube morphology.