Cholelithiasis prevalence and risk factors in individuals with severe or profound intellectual and motor disabilities.

BACKGROUND: The prevalence and risk factors of cholelithiasis in individuals with severe or profound intellectual and motor disabilities (SPIMD) are poorly characterised. Thus, we aimed to investigate the prevalence and risk determinants of cholelithiasis in a cohort with SPIMD under medical care in a residential facility. METHODS: We categorised 84 patients in a residential hospital for persons with SPIMD into groups: those with (Group CL) and without (Group N) cholelithiasis. Gallstones were detected via computed tomography, ultrasonography or both. We evaluated gastrostomy status, nutritional and respiratory support, constipation, and bladder and kidney stones. Data were significantly analysed using univariate and multivariate logistic regression analyses. RESULTS: The prevalence rate of cholelithiasis in our SPIMD cohort was 27%. There were no significant differences in sex, age, weight, height, or Gross Motor Function Classification System between the two groups. However, more patients received enteral nutrition (39.13% vs. 6.56%; P = 0.000751) and were on ventilator support (56.52% vs. 19.67%; P = 0.00249) in Group CL than in Group N. Enteral nutrition [odds ratio (OR) 10.4, 95% confidence interval (CI) 1.98-54.7] and ventilator support (OR 20.0, 95% CI 1.99-201.0) were identified as independent risk factors for the prevalence of cholelithiasis in patients with SPIMD. CONCLUSIONS: Patients with SPIMD demonstrated an increased prevalence of cholelithiasis, with a notable association between nutritional tonic use and respiratory support. Therefore, to emphasise the need for proactive screening, it is crucial to devise diagnostic and therapeutic strategies specific to patients with SPIMD. Further investigation is essential to validate our findings and explore causative factors.

Molecular species of phospholipid in rat hepatomas and in fetal, regenerating, and adult rat livers.

The molecular species of phospholipid in rat hepatomas were found to be different from those in normal adult liver. Phosphatidylcholine in Yoshida hepatoma contained phosphatidylcholine with 34:1 as the sums of the chain length and of the unsaturation of fatty acids esterified at C-1 and C-2 of glycerol, as an example (PC34:1), PC36:2, PC36:1, PC34:2, and PC36:3, and its phosphatidylethanolamine contained PE36:2, PE36:1, PE38:4, PE36:3, and PE34:1 as major species, whereas phosphatidylcholine in normal adult liver contained PC38:4, PC36:2, PC34:2, PC36:4, and PC34:1, and its phosphatidylethanolamine (PE) contained PE38:4, PE38:6, PE40:6, PE36:4, and PE36:2, with their level decreasing in that order. While Morris hepatoma also had significantly lower amounts of species containing polyunsaturated fatty acids, there were higher levels of those phosphoglycerides containing monoenoic and dienoic fatty acids. Regenerating liver showed similar patterns of molecular species of both phospholipids to those of normal liver. In contrast, fetal liver had similar molecular species of phosphatidycholine to those of hepatomas, but had similar species of phosphatidylethanolamine to those of normal and regenerating livers.

Identification of the functional region on the superantigen Yersinia pseudotuberculosis-derived mitogen responsible for induction of lymphocyte proliferation by using synthetic peptides.

Yersinia pseudotuberculosis-derived mitogen (YPM) is the unique Gram-negative bacillary superantigen known. In order to identify the regions on the YPM molecule involved in its superantigenic activity, seven overlapping peptides of the entire YPM molecule were synthesized and tested to evaluate their effects on the YPM-induced proliferation of human peripheral blood lymphocytes. A peptide corresponding to the N-terminal amino acid sequence (1-23) was found to inhibit YPM-induced lymphocyte proliferation in a concentration-dependent manner. The N-terminal peptide was found to show no inhibition of the proliferation induced by the other superantigen (staphylococcal enterotoxin B) or the other T-cell mitogen pertussis toxin, indicating that the inhibition is specific to YPM-induced proliferation. Thus, we have identified the N-terminal region (1-23) of the YPM as one of the functional regions responsible for its superantigenic activity.

Steroid hormones induce macrophage colony-stimulating factor (MCSF) and MCSF receptor mRNAs in the human endometrium.

We investigated the biological effects of sex-steroid hormones, secreted from the corpus luteum and placenta, on the induction of mRNAs encoding macrophage colony-stimulating factor (MCSF) and c-fms proto-oncogene (MCSF receptor) in human endometrium. RNA was extracted from the placenta and endometrium of both pregnant and non-pregnant women, and Northern blot analysis was performed on poly(A)+ RNA using MCSF or c-fms proto-oncogene cDNA as the probe. Results showed: (1) that MCSF mRNA was expressed in the placenta and endometrium of the pregnant uterus, (2) that c-fms proto-oncogene mRNA was also expressed in the placenta and endometrium of the pregnant uterus, and (3) that exogenous sex-steroid hormones could induce the expression of MCSF and c-fms proto-oncogene mRNAs in the endometrium of non-pregnant women. These results indicate that sex-steroid hormones secreted by the corpus luteum and/or placenta influence endometrial and placental growth and differentiation via a mechanism of action involving local production of MCSF and its receptor.

Satisfaction of patients treated surgically for intractable aspiration.

STUDY OBJECTIVE: Impaired laryngeal protective function can result in intractable aspiration requiring surgical treatment. There are, however, few reports evaluating the satisfaction of patients and the efficacy of surgical therapy. The purpose of this study is to determine whether surgery for intractable aspiration is beneficial for alleviating depression and improving the mood of patients who have undergone surgical treatment and whether patients and their families are satisfied with the therapy. PATIENTS AND STUDY DESIGN: Seven patients with recurrent aspiration pneumonia that could not be controlled by appropriate medical therapies participated in the study. These patients had no hope of recovering laryngeal function. Six underwent laryngectomy and one underwent laryngotracheal separation. After surgery, we evaluated the efficacy of the therapy and the patients' satisfaction with the therapy. METHODS: The following clinical variables concerning surgical procedure were examined: operation time, time until oral intake, videofluorographic study, and surgical complications. The treatment methods including feeding status were also examined before and after surgery. In addition, the following markers were examined to evaluate the efficacy of the surgery: score of aspiration pneumonia, body mass index, total protein, albumin, hematocrit, WBC count, C-reactive protein, erythrocyte sedimentation rate, and the Barthel Index, an indicator of daily activity. Furthermore, the grade of depression and mood, and satisfaction of patients and their caretakers among family members were scored by the Zung self-rating depression scale, a 20-picture face scale, and the visual analog scale. RESULTS: After surgical therapy, we confirmed by videofluorography that aspiration was completely prevented. No surgical complications occurred. By 18 +/- 6 days, all seven patients were able to ingest a meal orally. The need for extensive medical care and repeated hospitalizations became unnecessary after surgery. The control of pneumonia and albumin improved significantly. The grade of depression and mood of patients and their families also improved significantly. Satisfaction scores of patients receiving therapy were very high. CONCLUSIONS: Our study shows that surgical therapy to prevent aspiration improves the depression and mood of patients and their families as well as feeding status and clinical outlook. Surgical therapy for patients with intractable aspiration is effective and beneficial.

Cytokine production in chorioamnionitis.

Lymphohematopoietic cytokines play a significant role in many biological mechanisms including a number of reproductive processes such as ovulation, implantation, placentation, cervical dilation and parturition. Recent experiments have suggested that cytokines play a crucial role in the mechanisms of preterm labor and delivery, which are the leading causes of perinatal morbidity and mortality. Growing evidence suggests that infection is deeply concerned in the pathogenesis of preterm labor and delivery. Chorioamnionitis, a subset of intrauterine infection, has been identified in 20-33% of women with preterm delivery, and the inflammatory and related cytokines, interleukin-1 (IL-1), tumor necrosis factor-alpha (TNF-alpha), interleukin-6 (IL-6) and interleukin-8 (IL-8), showed substantial increases in the amniotic fluid at women with intrauterine infection. Although the precise mechanism for chorioamnionitis-driven preterm labor mediated via cytokines is still unknown, both IL-1 and TNF-alpha along with IL-6 enhance prostaglandin production by human amnion cells, chorionic cells and decidual cells. Analysis of the regulatory sequences in the 5' upstream regions of receptor gene for human oxytocin, a potent uterotonic agent, suggests a close relationship between preterm labor and inflammatory cytokines through induction at the oxytocin receptor. Prompt identification of the patients with intra-amniotic infection may be useful in clinical practice. At present, the measurement of IL-8 in maternal serum or the measurement of IL-6 in cervical secretion may be helpful as a non-invasive screening for chorioamnionitis.

pH dependence of the binding constant of Ca2+ to the phospholipase A2 of A. halys blomhoffii. Participation of ionizable groups with pK values of 5.16, 6.45, and 7.30.

The pH dependence of the binding constant of Ca2+ to the phospholipase A2 of A. halys blomhoffii was studied at 25 degrees C and an ionic strength of 0.1 by the tryptophyl fluorescence method and aromatic circular dichroism (Ikeda and Samejima (1981) J. Biochem. 89, 1175-1184), and was compared with those for cobra venom phospholipases A2 (Teshima et al. (1981) J. Biochem. 89, 13-20) and for porcine pancreatic enzyme (Pieterson et al. (1974) Biochemistry 13, 1439-1445). The shape of the pH-dependence curve was closer to that for the porcine enzyme than those for the cobra enzymes. The data were analyzed on the basis of our previous findings (Ikeda and Samejima (1981) J. Biochem., 90, 799-804) that the pK value of the ionizable group (alpha-amino group) is perturbed from 7.30 to 6.30 on the Ca2+ binding, and that the protonation of another group corresponding to Asp 49 of the porcine enzyme with a pK value of 5.16 competes with the Ca2+ binding. An additional ionizable group with a pK value of 6.45 was found to participate in the Ca2+ ion binding, and this was assigned to the His residue corresponding to His 48 in the active site of the porcine enzyme.

pH dependence of the binding constant of a phospholipase A2 from Agkistrodon halys blomhoffii venom to micelles of n-hexadecylphosphorylcholine.

The phospholipase A2 from the venom of A. halys blomhoffii was titrated with micellar n-hexadecylphosphorylcholine (an analog of lysolecithin) by following the tryptophyl fluorescence change at 25 degrees C and ionic strength 0.1. The data were analyzed by assuming that the micellar surface has multiple binding sites for the enzyme and that these sites are identical and mutually independent. The enzyme binding site was found to accommodate a constant number of the substrate (monomer) molecules, N = 10.0 and 6.7 for the apoenzyme and its Ca2+ complex, respectively. The binding constant of the enzyme to the substrate micelle was found to be enhanced by Ca2+ binding to the enzyme. The pH dependence of the binding constant of the apoenzyme to the micelle was well interpreted in terms of pK shifts of two ionizable groups from 5.16 to 5.67 and from 6.45 to 6.6. The pH-dependence curve for the enzyme-Ca2+ complex, which lacked the former transition, was interpreted in terms of the pK shift of a single ionizable group from 5.55 to 5.76. The former ionizable group was assigned as Asp 49, to which Ca2+ ion can coordinate, and the latter as His 48 in the active site. No participation of the alpha-amino group with a pK value of 7.30 was observed. The binding constant of the enzyme to the substrate micelle, Kmic = 0.45-2.3 X 10(6) M-1, was found to be far greater than that to the monomeric substrate, Kmon = 0.2-1.0 X 10(4) M-1. This was interpreted in terms of the presence of an additional weak substrate-binding site in the enzyme molecule.

Kinetics of the hydrolysis of mixed micelles of dipalmitoyllecithin with triton X-100 catalyzed by a phospholipase A2 from the venom of Agkistrodon halys blomhoffii.

The pH dependence of kinetic parameters for the hydrolysis of mixed micelles of 1,2-dipalmitoyl-sn-glycero-3-phosphorylcholine (diC16PC) with Triton X-100, catalyzed by the intact and the N-terminal alpha-NH2-modified phospholipases A2 (PLA2s) of Agkistrodon halys blomhoffii, was studied at 25 degrees C and ionic strength 0.1 in the presence of saturating amounts of Ca2+. The pH dependence of the kinetic parameters for the hydrolysis of monodispersed diC6PC, catalyzed by the modified enzyme, was also studied under the same conditions, and the data were compared with the previous results for the intact enzyme [Teshima, K. et al. (1986) J. Biochem. 100, 1655-1662]. The pK values of the catalytic group, His 48, and Tyr 52 were found to shift from 5.55 to 7.00 and from 10.50 to 11.50, respectively, on binding of the micellar substrates to the enzyme. On the other hand, no participation of these ionizable groups was observed for the binding of the monodispersed substrate. On the basis of the present finding and the X-ray crystallographic studies on bovine pancreatic PLA2 [Dijkstra, B.W. et. al. (1981) J. Mol. Biol. 147, 97-123] and on a PLA2 of Crotalus atrox venom [Brunie, S. et al. (1985) J. Biol. Chem. 260, 9742-9749], the hydrogen-bonding of Tyr 73, which is involved in the lipid-water interface recognition site, to His 48 and Tyr 52 in the active center was strongly suggested to be important for the hydrolysis of micellar substrates.

Kinetics of the hydrolysis of monodispersed dihexanoyllecithin catalyzed by the phospholipase A2 from Agkistrodon halys blomhoffii venom.

The hydrolysis of 1,2-dihexanoyl-sn-glycero-3-phosphorylcholine (diC6PC), catalyzed by the phospholipase A2 from the venom of Agkistrodon halys blomhoffii, was studied at 25 degrees C and the ionic strength of 0.1 in the presence of 3-33.3 mM Ca2+, which can saturate the Ca2+-binding site of the enzyme. The initial velocity data, obtained at various concentrations of the substrate below the critical micelle concentration (cmc), were analyzed according to the Michaelis-Menten equation. The pH-dependence curve of the Km value exhibited only one transition below pH 8. The analytical results indicated that the pK value of 6.30 of an ionizable group changed to 6.54 on the binding of the monodispersed substrate. This ionizable group was assigned as the alpha-amino group on the basis of its pK value, which had been determined from the pH dependence of the binding constant of monodispersed n-dodecylphosphorylcholine (n-C12PC) (Ikeda and Samejima (1981) J. Biochem. 90, 799-804, and Haruki et al. (1986) J. Biochem. 99, 99-109). The pH-dependence curve of the kcat value exhibited two transitions, below pH 6.5 and above pH 9.5. The analytical results indicated the participation of two ionizable groups with pK values of 5.55 and 10.50. Deprotonation of the former and protonation of the latter group were found to be essential for the catalysis. The former ionizable group was assigned as His 48 in the active site on the basis of its pK value, which had been determined from the pH dependence of the binding constant of Ca2+ (Ikeda et al. (1981) J. Biochem. 90, 1125-1130).(ABSTRACT TRUNCATED AT 250 WORDS)

Interaction of monodispersed and micellar phospholipids with an Agkistrodon halys blomhoffii phospholipase A2, in which the alpha-amino group had been modified to an alpha-keto group.

The pH dependence of the binding constant of Ca2+ to a phospholipase A2 of Agkistrodon halys blomhoffii, in which the alpha-amino group had been selectively modified to an alpha-keto group, was studied at 25 degrees C and ionic strength 0.1 by the tryptophyl fluorescence method. The dependence was compared with the results for the intact enzyme (Ikeda et al. (1981) J. Biochem. 90, 1125-1130). The pH-dependence curve could be well interpreted in terms of the participation of the two ionizable groups Asp 49 and His 48, with pK values of 4.70 and 6.69, respectively. These values were slightly different from the respective pK values for the intact enzyme, 5.15 and 6.45. Ca2+ binding to the intact enzyme involves the participation of an additional ionizable group with a pK value of 7.30, which was thus assigned as alpha-amino group. The pH dependence of the binding constant of monodispersed n-dodecylphosphorylcholine (n-C12PC) to the alpha-NH2-modified enzyme was studied at 25 degrees C and ionic strength 0.1 by the aromatic circular dichroism (CD) method. The pH-dependence curve for the modified apoenzyme was interpreted as reflecting the participation of a single ionizable group with a pK value of 4.7, which was assigned to Asp 49 (to which a Ca2+ ion can coordinate) since the curve for the Ca2+ complex lacked this transition: the binding constant was independent of pH. The pH-dependence curves for the intact apoenzyme and its Ca2+ complex involve the participation of an additional ionizable group with pK values of 7.30 and 6.30, respectively (Ikeda & Samejima (1981) J. Biochem. 90, 799-804), which was assigned as the alpha-amino group. The hydrolysis of monodispersed 1,2-dihexanoyl-sn-glycero-3-phosphorylcholine (diC6PC), catalyzed by the intact and the alpha-NH2-modified enzymes was studied by the pH stat method at 25 degrees C, pH 8.2, and ionic strength 0.1 in the presence of 3 mM Ca2+. The Km value for the modified enzyme was found to be very similar to that for the intact enzyme: this was compatible with the results of the direct binding study on the monodispersed n-C12PC under the same conditions. However, the kcat value was about 43% of the value for the intact enzyme, suggesting that the alpha-keto group introduced by the chemical modification perturbed the network of hydrogen bonds in the active site.(ABSTRACT TRUNCATED AT 400 WORDS)

Bindings of Ca2+ and substrate analogs to a cobra venom phospholipase A2 in which the alpha-amino group is modified to an alpha-keto group.

The pH dependence of the chemical reaction rate of p-bromophenacyl bromide (BPB) with His 48 of cobra (Naja naja atra) venom phospholipase A2, in which the alpha-NH2 group had been selectively modified to an alpha-keto group, was studied at 25 degrees C and ionic strength 0.1 in the absence of Ca2+. The pH-dependence curve was monophasic with a midpoint at pH 7.9, which corresponds to the pK value of His 48 of the alpha-NH2-modified enzyme, whereas the curve for the intact enzyme was biphasic, indicating participation of two ionizable groups with pK values of 7.3 and 8.55 (Teshima et al. (1982) J. Biochem. 91, 1778-1788). These two groups were thus identified as His 48 and the alpha-NH2 group, respectively. The pH dependence of the binding constant of Ca2+ to the alpha-NH2-modified enzyme was studied at 25 degrees C and ionic strength 0.1 by measuring the tryptophyl fluorescence changes. The pH-dependence curve was very similar to that for the intact enzyme (Teshima et al. (1981) J. Biochem. 89, 13-20), and it was interpreted in terms of participation of His 48 and Asp 49 (pK 5.4). The absence of participation of the alpha-NH2 group in the Ca2+ binding was thus confirmed. Bindings of monodispersed n-dodecylphosphorylcholine (n-C12PC) and micellar n-hexadecylphosphorylcholine (n-C16PC) to the alpha-NH2-modified enzyme were studied at 25 degrees C and ionic strength 0.1 by the aromatic circular dichroism (CD) and tryptophyl fluorescence methods, respectively. The binding constant of the monodispersed substrate was very similar to that for the intact enzyme (Teshima et al. (1981) J. Biochem. 89, 1163-1174). The binding constant of the micellar substrate to the modified enzyme in the presence of Ca2+ was also very similar to that for the intact enzyme-Ca2+ complex (Teshima et al. (1983) J. Biochem. 94, 223-232), and the pH-dependence curve was interpreted in terms of participation of His 48. On the other hand, the binding constant of the micellar substrate to the modified apoenzyme was much smaller than that for the intact apoenzyme. Nevertheless, the pH-dependence curve could be interpreted in terms of participation of His 48 and Asp 49. From these findings, it was concluded that the ionization state of the alpha-NH2 group of cobra venom phospholipase A2 is essentially irrelevant to the bindings of Ca2+ and also of the monodispersed and micellar substrates.

Kinetics of the hydrolysis of monodispersed dihexanoyllecithin catalyzed by a cobra (Naja naja atra) venom phospholipase A2.

The hydrolysis of 1,2-dihexanoyl-sn-glycero-3-phosphorylcholine (diC6PC), catalyzed by a cobra (Naja naja atra) venom phospholipase A2, was studied at 25 degrees C ionic strength 0.1 in the presence of 3-10 mM Ca2+, which can saturate the Ca2+-binding site of the enzyme. The initial velocity data, obtained at various concentrations of the substrate below the critical micellar concentration (cmc), were analyzed according to the Michaelis-Menten equation. The Km value was practically independent of pH (between pH 6.75 and 10.30). This finding was consistent with the result of a direct binding study on monodispersed n-alkylphosphorylcholines (Teshima et al. (1981) J. Biochem. 89, 1163-1174). The hydrolysis of the substrate was competitively inhibited by the presence of monodispersed n-dodecylphosphorylcholine (n-C12PC). These results indicated that the substrate and n-C12PC compete for the same site on the enzyme molecule. The pH dependence curve of the kinetic parameter, kcat/Km, exhibited three transitions, below pH 8, between pH 8 and 9.5, and above pH 10. The analysis indicated the participation of three ionizable groups with pK values of 7.25, 8.50, and 10.4. The deprotonation of the first group and the protonation of the third group were found to be essential for the catalysis. The first group was assigned as His 48 in the active site on the basis of its pK value, which had been determined from the pH dependence of the binding constant of Ca2+ (Teshima et al. (1981) J. Biochem. 89, 13-20).(ABSTRACT TRUNCATED AT 250 WORDS)

Crystallization and preliminary X-ray study of Agkistrodon halys blomhoffii phospholipase A2 complexed with a specific inhibitor.

Phospholipase A2 from the venom of Agkistrodon halys blomhoffii has been crystallized as a complex with a specific inhibitor, (S)-2-dodecanoyl-amino-3-hexanol-1-phosphoglycol. The complex crystals belong to the hexagonal space group, P6(1)22 (or P6(5)22), with cell dimensions of a = b = 61.13 A, and c = 173.15 A. The diffraction extends to at least 2.3 A resolution.

Kinetics of the hydrolysis of micellar substrates catalyzed by snake venom phospholipases A2.

Effects of Ca2+ on the kinetic parameters for the hydrolysis of mixed micelles of 1,2-dipalmitoyl-sn-glycero-3-phosphorylcholine (diC16PC) with Triton X-100, catalyzed by a cobra (Naja naja atra) (Group I) and a Habu (Trimeresurus flavoviridis) (Group II) PLA2s, were studied and compared with the results reported for other Group I and II enzymes. The substrate bindings to Group I enzymes were independent of the Ca2+ binding, whereas the substrate bindings to Group II enzymes were facilitated more than 10 times by the Ca2+ binding to the enzymes. The result for Group II enzymes, but not Group I enzymes, seemed compatible with the hypothesis for interpreting the catalytic mechanism that an intermediate complex should be stabilized by the coordination of the bound Ca2+ with the phosphoryl group and the carbonyl oxygen atom of the ester bond at the sn-2 position of the bound substrate molecule [Verheij et al. (1980) Biochemistry 19, 743-750 and (1981) Rev. Physiol. Biochem. Pharmacol. 91, 91-203]. The pH dependence of the kinetic parameters for the hydrolysis of the mixed micellar diC16PC, catalyzed by the cobra (N. naja atra) (Group I) and Habu (T. flavoviridis) (Group II) PLA2s, was also studied. The pK values of the catalytic group, His 48, and Tyr 52 for N. naja atra PLA2, shifted from 7.25 to 7.70 and from 10.30 to 10.85, respectively, and the corresponding values for T. flavoviridis PLA2 shifted from 5.80 to 6.95 and from 10.10 to 10.76, respectively, on binding of the micellar substrates to the enzymes.(ABSTRACT TRUNCATED AT 250 WORDS)

Isolation and fundamental properties of a phospholipase A2 inhibitor from the blood plasma of Trimeresurus flavoviridis.

Phospholipase A2 inhibitor was purified from the blood plasma of Habu, Trimeresurus flavoviridis, by Sephadex G-200 gel filtration, DEAE-cellulose chromatography, and Blue-Sepharose CL-6B column chromatography. The purified inhibitor was shown to be a glycoprotein with a molecular weight of about 100K. It was found to consist of four subunits whose molecular weights were around 20-24K. In order to examine the inhibition mechanism of the inhibitor, the interaction of the inhibitor with a phospholipase A2 from T. flavoviridis venom was examined by Sephadex G-100 gel filtration. One inhibitor molecule was found to bind directly to one phospholipase A2 molecule in both the presence and absence of Ca2+. The inhibitor inhibited the phospholipase A2 from T. flavoviridis venom with an apparent dissociation constant, Ki, of 1.7 X 10(-10) M, but not the porcine pancreas enzyme or the Agkistrodon halys blomhoffii enzyme belonging to the same family, Crotalidae, as T. flavoviridis, or the phospholipase C from Bacillus cereus.

pH dependence of the reaction rate of His 48 with p-bromophenacyl bromide and of the binding constant to Ca2+ of the monomeric forms of intact and alpha-NH2 modified phospholipases A2 from Trimeresurus flavoviridis.

The phospholipase A2 of Trimeresurus flavoviridis was found to show monomer-dimer equilibria. Under conditions where the enzyme exists predominantly in the monomeric form, the chemical reaction rate of p-bromophenacyl bromide (BPB) with the catalytic group, His 48, was studied at 25 degrees C and ionic strength 0.2 by measuring the residual enzymic activity using a fluorescent substrate, 1,2-bis[4-(1-pyreno)butanoyl]-sn-glycero-3-phosphorylcholine (diPBPC). The pH-dependence curve of the reaction rate for the intact enzyme was practically the same as that for the modified enzyme, in which the N-terminal alpha-NH2 group had been selectively converted into an alpha-keto group. The pH-dependence curves were monophasic (sigmoidal) with a midpoint at pH 7.53, which corresponds to the pKa value of His 48. The pH dependences of the binding constants of Ca2+ to the intact and the alpha-NH2 modified enzymes were also studied at 25 degrees C and ionic strength 0.2 by measuring the changes in the tryptophyl fluorescence and/or aromatic CD spectra. The pH-dependence data for the modified enzyme were interpreted in terms of participation of Asp 49 (pKa 5.40) and His 48 (pKa 7.53), assuming that the protonation of Asp 49 competes with the Ca2+ binding. The pH-dependence data for the intact enzyme were similarly interpreted in terms of participation of the alpha-NH2 group (pKa 9.40) in addition to that of Asp 49 (pKa 5.40) and His 48 (pKa 7.53).(ABSTRACT TRUNCATED AT 250 WORDS)

Binding mode of phospholipase A2 with a new type of phospholipid analog having an oxazolidinone ring.

Inhibition of phospholipases A2 (PLA2s) by a new type of monodispersed phospholipid analog, 3-dodecanoyl-4-phosphatidylcholinohydroxymethyl-2-oxazolidinone (oxazolidinone-PC), was investigated by the pH stat assay method using monodispersed 1,2-dihexanoyl-sn-glycero-3-phosphorylcholine (diC6PC) as the substrate. The PLA2s used were those from bovine pancreas and cobra (Naja naja atra) venom (Group I) and from Japanese mamushi (Agkistrodon halys blomhoffii) venom (Group II). This new-type substrate analog was shown to inhibit competitively both types of venom and bovine pancreatic enzymes by binding to the active site in a similar manner to the carboxamide-type analog 2-dodecanoyl-amino-1-hexanol-phosphocholine (amide-PC). The binding of a stereoisomer, (R)-amide-PC, to N. naja atra (Group I) and A. halys blomhoffii (Group II) PLA2s was facilitated by the binding of Ca2+ to the enzymes. On the other hand, the binding of (R)-oxazolidinone-PC to the N. naja atra (Group I) enzyme was found to be independent of Ca2+ binding, while its binding to the A. halys blomhoffii (Group II) enzyme was markedly facilitated by the binding of Ca2+ to the enzyme. The binding of (R)-amide-PC to N. naja atra PLA2 (Group I) was markedly influenced by the ionization state of the catalytic residue His 48, whereas the binding of (R)-oxazolidinone-PC was found to be practically independent of the ionization state of this residue.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of Ca2+ in the binding of phospholipase A2 with a monomeric substrate and with its amide-type analog.

Effects of Ca2+ on the kinetic parameters for the hydrolysis of monodispersed 1,2-dihexanoyl-sn-glycero-3-phosphorylcholine (diC6PC), catalyzed by Group I phospholipases A2 (PLA2s) from Pseudechis australis, Naja naja atra, and bovine pancreas and by Group II enzymes from Vipera russelli russelli, Agkistrodon halys blomhoffii, and Trimeresurus flavoviridis, were studied by the pH-stat assay method at 25 degrees C, pH 7.5-8.2, and an ionic strength of 0.1 or 0.2 in the absence or presence of an amide-type substrate analog, 2-dodecanoyl-amino-1-hexanol-phosphoglycol. The binding of genuine substrate to the Group II enzymes and that of its analog to the Groups I and II enzymes were markedly facilitated by the binding of Ca2+ to the enzymes. On the other hand, the binding of genuine substrate to the Group I enzymes was found to be independent of the Ca2+ binding. The former result suggests that the structures of the Group II enzyme-genuine substrate complexes and both types of enzyme-analog complexes are generally stabilized by the Ca2+ binding, whereas the latter indicates that the structures of the Group I enzyme-genuine substrate complexes are already similar to those of their Ca2+ complexes and that, therefore, these enzyme-substrate interactions are independent of the Ca2+ binding.

Role of Ca2+ in the substrate binding and catalytic functions of snake venom phospholipases A2.

Phospholipases A2 are classified into two groups, I and II, according to differences in the polypeptide-chain length and the intramolecular-disulfide bondings. The effects of Ca2+ on the kinetic parameters for the hydrolysis of monodispersed and micellar phosphatidylcholines, catalyzed by a cobra (Naja naja atra) enzyme (Group I) and by mamushi (Agkistrodon halys blomhoffii) and habu (Trimeresurus flavoviridis) enzymes (Group II), were studied by the pH-statassay method at 25 degrees C, pH 8.0-8.2, and ionic strength 0.1-0.2. The results were compared with those reported for the other Group I and II enzymes. The Ca2+ binding was clearly shown to be essential for the catalysis of all the phospholipases A2. However, the substrate binding to Group I enzymes was found to be independent of the Ca2+ binding. On the other hand, the substrate binding to Group II enzymes was facilitated more than 10 times by the binding of Ca2+ to the enzymes. This was interpreted in terms of conformation changes of the peptide loop of residues 26 to 44 accompanying the Ca2+ binding. The latter result, but not the former, seems compatible with the hypothesis for interpreting the catalytic mechanism of phospholipases A2 that an intermediate complex should be stabilized by the coordination of the bound Ca2+ ion with the phosphoryl group and the carbonyl oxygen atom of the ester bond at the sn-2 position of the bound substrate molecule [Verheij et al. (1980) Biochemistry 19, 743-750 and (1981) Rev. Physiol. Biochem. Pharmacol. 91, 91-203]. According to the similarity in the primary and tertiary structures of the active sites of both types of enzymes [Renetseder et al. (1985) J. Biol. Chem. 260, 11627-11634], it is supposed that similar intermediate complexes may occur even for Group I enzymes, at least in the transition state of the productive complexes.