Direct vesicle-vesicle exchange of phospholipids mediated by polymyxin B

Direct and rapid intermembrane exchange of phospholipids without fusion is shown to occur across stable vesicle-vesicle contacts formed by stoichiometric amounts of polymyxin B. The exchange is selective for monoanionic, but not dianionic, glycerophospholipids irrespective of their chain length or phase properties. Selective transfer mediated by protein contacts between membranes could serve as a model for stable fusion intermediates and provide a structural and organizational basis for direct phospholipid transfer as implicated in entry of enveloped viruses, secretion, endocytosis, and intracellular transport and targeting of lipids. It is also proposed that the loss of the specificity of phospholipid composition in the inner and outer membranes of gram negative bacteria mediated by polymyxin B could be the basis for its bactericidal action.

Successful treatment of antimony-resistant visceral leishmaniasis with liposomal amphotericin B (L-AmpB-LRC) in a child

Visceral leishmaniasis continues to be a major health problem in Bihar and West Bengal states of India. In Bihar almost 44 million people in 28 districts and in West Bengal 5.5 million people in eight districts are at risk of visceral leishmaniasis1. Pentavalent antimonial (Sbv) compounds are the first-line drugs, and amphotericin B is used when failure to respond to antimony occurs2. We report the case of a 7-year-old boy with advanced antimony-resistant visceral leishmaniasis who was successfully treated by liposomal amphotericin B (L-AmpB-LRC) manufactured in our institute. This case report documents the efficacy of L-AmpB-LRC in such a patient and highlights the need for a longer duration of treatment.

Impaired pancreatic bicarbonate secretion in chronic malnutrition

Twenty three children with recurrent episodes of diarrhea and chronic malnutrition were studied for pancreatic duct function. Those children were subjected to pancreatic stimulation with pancreozymin and secretin. Grade I malnourished children, as per Gomez classification, formed the control group. The water output from pancreas increased in malnourished children (p < 0.05). It correlated significantly to cationic transport (p < 0.01). Sodium and potassium together accounted for significant proportion of water output in pancreatic fluid. Potassium transport increased with increasing severity of malnutrition and may be responsible for the hypokalemia observed in malnourished children. Pancreatic secretion of bicarbonate decreased in severe malnutrition inspite of increased flow rate of pancreatic secretion. This is probably due to defective bicarbonate secretion likely to be located at pancreatic duct epithelial cell membrane.

Phospholipase A2 engineering. Structural and functional roles of the highly conserved active site residue aspartate-49

Site-directed mutagenesis and high-resolution two-dimensional (2D) proton nuclear magnetic resonance (NMR) were used to probe the structural and functional roles of a highly conserved residue, Asp-49, in the interfacial catalysis by bovine pancreatic phospholipase A2 (PLA2, overexpressed in Escherichia coli). According to crystal structures, the side chain carboxylate of Asp-49, along with the carbonyl oxygens of Tyr-28, Gly-30, and Gly-32, and two water molecules, provides the necessary ligands for Ca2+ which is essential for the enzymatic activity. The Asp-49 of PLA2 was changed to Asn, Glu, Gln, Lys, and Ala; the resulting mutants are named D49N, D49E, D49Q, D49K, and D49A, respectively. The conformational stabilities of all five mutants are similar to that of WT as judged by guanidine hydrochloride-induced denaturation. The structural analyses by NMR indicated no global perturbations upon substitutions, although localized conformational perturbations can be observed for less conserved replacements. Direct Ca2+ binding studies showed no specific binding for D49A, D49N, D49Q, and D49K; however, D49E retains a 12-fold weaker calcium binding affinity (Kd,Ca = 23 mM). The specific activities of all five mutant enzymes decrease significantly, ranging from 5.4 x 10(2)- to 5.8 x 10(5)-fold in comparison with that of the wild-type enzyme. The observed activities of mutants require the presence of Ca2+. This demonstrates the functional importance of Asp-49 in the catalytic mechanism of PLA2, presumably by helping to bind and properly orient Ca2+.(ABSTRACT TRUNCATED AT 250 WORDS)

Purification and characterization of a calcium-independent acidic phospholipase A2 from rat lung

Several phospholipase A2 (PLA2) activities have been identified in rat lung homogenate and shown to be important in metabolism of lung phospholipids. One PLA2 activity is Ca(2+)-independent, active in vitro at pH 4, and inhibited by a substrate analogue, 1-hexadecyl-3-trifluoroethylglycero-sn-2-phosphomethanol (MJ33). Purification of this rat lung PLA2 by approx. 550-fold was carried out by sequential column chromatographies using DE-52, Sephacryl-100, heparin-Sepharose, and phenyl-Sepharose columns. The purified activity had an acidic pH optimum, was Ca(2+)-independent, was inhibited by MJ33 in a dose-dependent manner (50% inhibition at 3 mol%), was unaffected by treatment with p-bromophenacyl bromide or mercaptoethanol, and had a unique N-terminal amino acid sequence. The apparent molecular mass was 15 kDa on gel electrophoresis and activity was recovered in part by renaturation of protein from the gel. The properties of this enzyme suggest a new class of PLA2.

Jejunal disaccharidases in protein energy malnutrition and recovery

The jejunal disaccharidases, sucrase, maltase and lactase, were determined in jejunal biopsies obtained from 43 malnourished children and 10 controls. In the study group, 63% were girls and 93% had severe malnutrition. Lactase activity was significantly reduced in third and fourth degree malnutrition (p < 0.05 and p < 0.005, respectively), but maltase activity was significantly reduced only in the fourth degree malnutrition (p < 0.01). After recovery, maltase and sucrase activities showed a marginally significant increase (p = 0.06), where lactase showed no significant increase (p > 0.05). We conclude that jejunal disaccharidase activity decreases significantly with increasing severity of malnutrition, lactase being the most severely affected and the last to recover.

A review of human immunodeficiency virus infection in India

By the turn of the century 20-50 million adults are projected to be HIV positive in Asia, and India will have the largest burden of newly infected patients in a single country. To determine the present status of the epidemic, a systematic review of available data in India has been carried out. Regional differences in reported HIV seroprevalence were found, with high levels in western, northeastern, and southern India and lower levels in northern, central, and eastern India. While differences in the temporal introduction of HIV may be partly responsible, the more likely explanation is incomplete data and reporting. In the past 4 years HIV has rapidly increased among commercial sex workers and patients coming to sexually transmitted diseases clinics in western (Bombay) and southern (Madras and Vellore) India. Assessing HIV seroprevalence in the general population is difficult because of limited data, especially from rural areas, where 60% of Indians reside. Heterosexual contact with commercial sex workers is the major reported risk factor, except in eastern India, where intravenous drug use is common. The impact of transfusions or contaminated needles is uncertain, but between 25 and 75% of blood donations are not screened for HIV, and 15% of infected patients had received transfusions. By October 1993, 494 cases of AIDS had been reported, but this number grossly underestimates the real situation since HIV is often unrecognized. Tuberculosis is the major HIV-associated infection. In its efforts to control HIV, India needs to institute a standardized surveillance system to provide data needed to design and implement appropriate interventions.

Inhibition of phospholipase A2

Phospholipases A2 are involved in inflammatory processes such as the liberation of free arachidonic acid from the membrane pool for the biosynthesis of eicosanoids. Inhibitors of these enzymes are proving useful in determining the biological roles of phospholipases A2 in complex cellular processes and may also have therapeutic potential. Inhibition of these lipolytic enzymes is more difficult to characterize as the enzymatic reaction occurs at a lipid/water interface. This review focuses on the description of a number of classes of rationally designed phospholipase A2 inhibitors. The development of a theoretical framework for the proper analysis of inhibitors is presented. Structural studies of phospholipase A2-inhibitor complexes suggest how the lipolysis reaction is catalyzed. Finally, some recent results on the use of phospholipase A2 inhibitors in living cells and tissues are revealed.

Tight binding inhibitors of 85-kDa phospholipase A2 but not 14-kDa phospholipase A2 inhibit release of free arachidonate in thrombin-stimulated human platelets

An analogue of arachidonic acid in which the COOH group is replaced by a trifluoromethyl ketone group (COCF3) has recently been shown to be a tight binding inhibitor of the 85-kDa cytosolic phospholipase A2 that is found in platelets and other cells (Street, I. P., Lin, H.-K., Laliberté, F., Ghomashchi, F. G., Wang, Z., Perrier, H., Tremblay, N. M., Huang, Z., Weech, P. K., and Gelb, M. H. (1993) Biochemistry 32, 5935-5940). This trifluoromethyl ketone inhibits most of the arachidonate release from the phospholipid pool in thrombin-stimulated human platelets at concentrations of 0-40 microM with 4 x 10(8) platelets/ml. A structure-function analysis of related compounds reveals a good correlation between the inhibition of the purified phospholipase A2 and the blockage of arachidonate release in platelets. A number of recently described potent inhibitors of the 14-kDa phospholipase A2 that is secreted from activated platelets have no effect on the level of free arachidonate production. Furthermore, the addition of a large amount of recombinant 14-kDa phospholipase A2 to platelets does not produce free arachidonate, and it does not alter the amount of arachidonate released following platelet activation with thrombin. These studies provide strong pharmacological evidence for the role of the cytosolic phospholipase A2 in producing most, if not all, of the liberated arachidonate in thrombin-stimulated human platelets, and they show that tight binding membrane-residing inhibitors of the cytosolic phospholipase A2 can block the eicosanoid cascade in living cells.

Characterization of interfacial catalysis by Aeromonas hydrophila lipase/acyltransferase in the highly processive scooting mode

A glycerophospholipid:cholesterol acyltransferase (GCAT) that also has lipase activity is secreted by the bacterium Aeromonas hydrophila. Hydrolysis of the sn-2-ester bond of 1,2-dimyristoyl-sn-glycero-3-phosphomethanol (DMPM) vesicles by this enzyme is shown to occur in a highly processive scooting mode in which the enzyme, substrate, and the products of hydrolysis remain bound to the vesicle interface. This conclusion is based on the following observations. (a) When there is an excess of vesicles over enzyme, the hydrolysis of the sn-2-acyl group ceases after only a fraction of the total available substrate is hydrolyzed. Addition of more enzyme, but not of more substrate, leads to a new round of hydrolysis. (b) The extent of hydrolysis of vesicles per enzyme increases with the size of the vesicles, and it corresponds to the total hydrolysis of the outer monolayer of one vesicle by one enzyme. (c) The enzyme bound to vesicles composed of reaction products or of the non-hydrolyzable phospholipid 1,2-ditetradecyl-sn-glycero-3-phosphomethanol (DTPM) is not able to undergo intervesicle exchange. Instead, intervesicle transfer of the substrate or the bound enzyme due to vesicle fusion promotes hydrolysis of all of the vesicles present in the reaction mixture. (d) Addition of DTPM vesicles to a reaction mixture containing DMPM substrate vesicles and the enzyme has no noticeable effect on the course of hydrolysis. Substrate specificity studies in the scooting mode on DMPM vesicles reveal that GCAT displays essentially no selectivity in the hydrolysis of phospholipids with different polar head groups. Treatment of GCAT with trypsin, which removes a small peptide, results in an enzyme that displays comparable catalytic activity but increased affinity for the interface. Alkyltrifluoromethyl ketones are shown to be tight-binding competitive inhibitors of GCAT. The scooting mode analysis, which has previously been shown to provide a simplified approach for analyzing the steady-state kinetics of interfacial catalysis by secreted phospholipase A2, is also useful for analyzing the interfacial kinetic behavior of lipases.

Functional significance of the conformational dynamics of the N-terminal segment of secreted phospholipase A2 at the interface

The kinetic and fluorescence properties of several pig pancreatic phospholipase A2 (PLA2) with substitutions and deletions in the N-terminal region and of tyrosines 52 and 73 are characterized. The substitutions Ala-1-D-Ala or -Gly, Trp-3-Phe, Gln-4-Nle, Arg-6-Glu, Tyr-52-Phe, and Tyr-73-Phe had at the most only a modest effect on the interfacial catalytic activity on the anionic interface to which they bind with high affinity. The observed rate of hydrolysis in the scooting mode by deletion mutants lacking one or more successive residues from the N-terminal region was lower by 50-95%. Detailed kinetic analysis of the deletion mutant lacking Ala-1 (des-1-AMPA) showed that the 50% decrease in the rate is due to a 5-fold increase in the interfacial Michaelis-Menten parameter, KM*, without a significant change in kcat. These results and direct measurements show that the primary effect of Ala-1 deletion is to lower the affinity for the active site directed ligands. Although the affinity of these mutants for anionic interface remains the same as for the wild type, the affinity for zwitterionic neutral diluents is considerably lower. Significant differences in the fluorescence quantum yields and the heterogeneity in the frequency-domain fluorescence intensity decays of these enzymes suggest that both in solution and at the interface the N-terminal region is an ensemble of conformations rather than a discrete state. Additional results suggest that the interfacial microenvironment of Trp-3 in des-1-AMPA is more polar and Trp-3 is more accessible to quenching by acrylamide.(ABSTRACT TRUNCATED AT 250 WORDS)

Phosphatidylinositol-specific phospholipase C from Bacillus cereus at the lipid-water interface: interfacial binding, catalysis, and activation

Binding characteristics of phosphatidylinositol-specific phospholipase C (PI-PLC) from Bacillus cereus binding to the phospholipid-water interface were determined by spectroscopic methods and correlated with PI-PLC's catalytic properties. Binding of the enzyme to micelles and bilayers of zwitterionic phosphocholines is accompanied by an increase in the fluorescence emission from tryptophan, whereas a decrease in the emission is observed with synthetic anionic lipids containing a phosphomethanol head group. A similar decrease in the tryptophan emission is observed with phosphatidylinositol (PI) analogues containing the phospho-D-1-myo-inositol head group, but not with the enantiomeric L-1-myo-inositol. In covesicles of PI and phosphatidylcholine (PC), the rate of cleavage of PI is reduced because, as a neutral diluent, PC effectively reduces the surface concentration of PI that the bound enzyme "sees" in the interface. This permits determination of the interfacial Michaelis constant (KM*) as 0.26 mol fraction for PI as substrate. On the other hand, ditetradecylglycerophosphomethanol (DTPM) acts as a kinetic competitive inhibitor in the covesicles. The spectroscopic and catalytic activity data taken together show that PI-PLC binds to the interface of aqueous dispersions of phospholipids with an apparent Kd (in terms of the lipid monomers) of about 10-50 microM. However, only lipids with an anionic head group, such as phosphomethanol and phospho-D-1-myo-inositol, are able to bind as single molecules into the active site of the enzyme at the interface. Enantiomeric phospho-L-1-myo-inositol or the zwitterionic phosphocholine head group has little affinity for the enzyme at the interface. Thus, PI-PLC appears to obey the two-stage, Michaelis-Menten adaptation of interfacial catalysis, according to which the binding of the enzyme to the interface precedes the steps of the catalytic turnover at the interface. Limit estimates suggest that on PI or PI/PC vesicles the catalysis occurs in the "scooting" mode with a moderate processivity. DTPM vesicles also inhibit the activity of PI-PLC toward the synthetic water-soluble substrate myo-inositol 1-(4-nitrophenyl phosphate), but the activity is enhanced severalfold in the presence of vesicles of zwitterionic phosphatidylcholine. Several possible explanations of this interfacial activation are considered within the general context of the kinetic scheme for interfacial catalysis. The kinetic results for the action of PI-PLC bound to vesicles are consistent with a model in which the interface acts as an "allosteric" effector of the catalytic rate constant, kcat, without affecting the substrate binding.

9p-Syndrome

A 2 1/2 month old male child was admitted with loose motions and mild dehydration. He was full term normal delivery, born of a non-consanguinous marriage. On examination, he had trigonocephaly; anteverted nostrils, long philtrum and hypoplastic supraorbital ridges. X-ray showed sutural separation. Karyotyping confirmed deletion of short arm of chromosome 9 distal to band p22.

Spectroscopic properties of the states of pig pancreatic phospholipase A2 at interfaces and their possible molecular origin

The near-UV absorption and fluorescence spectroscopic properties of Trp-3 of pig pancreatic phospholipase A2 (PLA2) in aqueous solution (E form) or at the interface without (E* form) or with a ligand at the active site (E*L form) are characterized. In the E form, the single tryptophan residue is exposed on the protein surface to the aqueous environment, as it is freely accessible to aqueous quenchers such as succinimide and acrylamide. The fluorescence quantum yield of E is about one-third that of N-acetyl-tryptophanamide, indicating significant intramolecular quenching processes including charge-transfer reactions, as seen by the D2O effect. Upon binding of PLA2 to micelles of 1-hexadecylpropanediol-3-phosphocholine (E*), a positive difference spectrum with a shoulder at 284 nm (delta epsilon = 370 M-1 cm-1) is observed. Similar difference spectra are also observed upon binding of sulfate ion to the E form. The fluorescence emission of E* is blue-shifted by about 10 nm to 336 nm, with a 2-fold higher quantum yield. Trp-3 in E* is significantly shielded from aqueous quenchers, and the D2O effect on the quantum yield is still present. The UV difference spectrum for the E*-to-E*L transition is of large amplitude with peaks at 292 (delta epsilon = 2540 M-1 cm-1) and 284 nm (delta epsilon = 2100 M-1 cm-1), which suggests transfer of tryptophan from an aqueous to a less polar environment. Upon conversion to the E*L form, there is a further blue shift to 333 nm, with about a 20% increase in the fluorescence quantum yield.(ABSTRACT TRUNCATED AT 250 WORDS)

Relationship of interfacial equilibria to interfacial activation of phospholipase A2

The equilibrium dissociation constants for the distribution of pig pancreatic phospholipase A2, its competitive inhibitors, and their complexes at the interface of a neutral diluent are determined. The relationship between these parameters and their significance for interfacial catalysis is elaborated in terms of a model based on the relationship between the underlying equilibria. By using a combination of spectroscopic and chemical modification methods, it was possible to determine the equilibrium dissociation constant of an inhibitor bound to the interface (K') or of the inhibitor bound to the enzyme in the aqueous phase (KI) or the interface (KI*). The equilibrium dissociation constant for the free enzyme (Kd) or for the enzyme-inhibitor complex (KdI) from the interface were also obtained. These constants are shown to be thermodynamically related, i.e., K'KdKI* = KIKdI, as predicted on the basis of the cyclic equilibrium scheme (thermodynamic box) describing the distribution of the enzyme and the inhibitor between the aqueous phase and the interface at constant calcium concentration. Results show that (i) calcium is required for the binding of a substrate or inhibitor molecule to the catalytic site; (ii) the effective dissociation constant of the inhibitor-enzyme complex in the aqueous phase is considerably larger than that for the enzyme at the interface, i.e., KI >> effective KI*; (iii) KdI does not depend on the structure of the inhibitor and Kd >> KdI; and (iv) structure-activity correlations suggest that ionic interactions between a ligand and the interfacial recognition site of the enzyme are important for K', which controls the concentration of the bound inhibitor that the enzyme "sees" in the interface. These observations demonstrate that the binding of the enzyme to the interface and the binding of the inhibitor to the active site of the enzyme at the interface are two distinguishable processes. Therefore, binding of a ligand to the active site of the enzyme promotes binding of the enzyme-inhibitor complex to other amphiphiles and the interface with higher affinity. It is suggested that the primary effect of binding the enzyme to the interface is to increase its intrinsic affinity toward the active-site-directed ligands, i.e., the interfacial activation of PLA2 is of K-type.

The chemical step is not rate-limiting during the hydrolysis by phospholipase A2 of mixed micelles of phospholipid and detergent

The effect of detergents on the overall catalytic turnover by secreted phospholipase A2 (PLA2) on codispersions of the substrate phospholipid is characterized. The overall rate of interfacial catalytic turnover depends on the effective substrate "concentration" (mole fraction) that the bound enzyme "sees" at the interface. Therefore, besides the intrinsic catalytic turnover rate determined by the Michaelis-Menten cycle in the interface [Berg et al. (1991) Biochemistry 30, 7283], two other interfacial processes significantly alter the overall effective rate of hydrolysis: first, the fraction of the total enzyme at the interface; second, the rate of replenishment of the substrate. At low mole fractions (< 0.3), bile salts promote the binding of pig pancreatic PLA2 to zwitterionic vesicles, and the rate of hydrolysis increases with the fraction of the enzyme in the interface. At higher (> 0.3) mole fractions of the detergent, the bilayer is disrupted, and the rate of hydrolysis decreases by more than a factor of 10. The detergent-dependent decrease in the rate of hydrolysis of the sn-2-oxyphospholipids is much larger than that of sn-2-thiophospholipid, and therefore the element effect (O/S ratio) decreases from about 10 in bilayers to less than 2 in mixed micelles. This loss of the element effect in mixed micelles shows that the chemical step is no longer rate-limiting during the hydrolysis of mixed micelles formed by the disruption of vesicles by the detergent. Such effects were observed with phospholipase A2 from several sources acting on substrates dispersed in a variety of detergents including bile salts, 2-deoxylysophosphatidylcholine, and Triton X-100.(ABSTRACT TRUNCATED AT 250 WORDS)

Interaction of sporidesmin, a mycotoxin from Pithomyces chartarum, with lipid bilayers

Sporidesmin, a mycotoxin from Pithomyces chartarum is a hydrophobic molecule. It can therefore be easily incorporated in the cell membrane, where it is likely to cause changes in the bilayer organization and the properties of membrane proteins. In order to understand the redox behaviour of sporidesmin in a hydrophobic environment, we have investigated the effects of oxidized and reduced sporidesmin on the phase transition properties of bilayers and on the susceptibility of bilayers to pancreatic phospholipase A2 (PLA2). The changes induced by sporidesmin in the thermotropic phase transition profiles of dimyristoyl-sn-3-phosphatidyl choline (DMPC) bilayers were similar to those caused by solutes known to localize in the glycerol-backbone region of the lipid bilayer, suggesting a similar localization for oxidized and reduced sporidesmin. Neither form of toxin disrupt the bilayer or membrane organization even at relatively high mole fractions. At concentrations < 10 mole% both forms partitioned equally well in the gel and liquid-crystalline phases, whereas at higher concentrations (approximately 30 mole%) reduced sporidesmin is preferentially localized in the liquid-crystalline phase. These effects of sporidesmin on the phase properties of DMPC vesicles were also reported by the fluorescence behavior of 10-pyrenedecanoic acid (PDA). The effects of oxidized and reduced sporidesmins on PLA2 kinetics are consistent with their ability to perturb bilayer organisation.

The divalent cation is obligatory for the binding of ligands to the catalytic site of secreted phospholipase A2

The divalent cation requirement for partial reactions of the catalytic turnover cycle during interfacial catalysis by pig pancreatic phospholipase A2 (PLA2) is investigated. Results show that the specific role of calcium in all the events of the catalytic cycle at the active site is not shared by other divalent cations. Cations such as calcium, barium, and cadmium bind to the enzyme in the aqueous phase. The active-site-directed ligands (substrate, products, and transition-state mimics) do not bind to the enzyme in the absence of a divalent cation. The synergistic binding of such ligands to the active site of PLA2 bound to the interface is, however, observed only in the presence of isosteric ions like calcium and cadmium, but not with larger ions like strontium or barium. The equilibrium constants for ligands bound to the enzyme in the presence of calcium and cadmium are virtually the same. However, only calcium supports the catalytic turnover; the rate of hydrolysis in the presence of cadmium is less than 1% of that observed with calcium. The role of divalent ions on the interfacial catalytic turnover cycle of PLA2 is not only due to the cation-assisted binding of the substrate but also due to its participation in the chemical step. Other roles of divalent ions in the events of interfacial catalytic turnover are also identified. For example, the binding of the enzyme to the interface is apparently promoted because the divalent cation is required for the sequential step, i.e., the binding of the substrate to the active site of PLA2.(ABSTRACT TRUNCATED AT 250 WORDS)

Biology, ecology, and biotechnological applications of anaerobic bacteria adapted to environmental stresses in temperature, pH, salinity, or substrates

Anaerobic bacteria include diverse species that can grow at environmental extremes of temperature, pH, salinity, substrate toxicity, or available free energy. The first evolved archaebacterial and eubacterial species appear to have been anaerobes adapted to high temperatures. Thermoanaerobes and their stable enzymes have served as model systems for basic and applied studies of microbial cellulose and starch degradation, methanogenesis, ethanologenesis, acetogenesis, autotrophic CO2 fixation, saccharidases, hydrogenases, and alcohol dehydrogenases. Anaerobes, unlike aerobes, appear to have evolved more energy-conserving mechanisms for physiological adaptation to environmental stresses such as novel enzyme activities and stabilities and novel membrane lipid compositions and functions. Anaerobic syntrophs do not have similar aerobic bacterial counterparts. The metabolic end products of syntrophs are potent thermodynamic inhibitors of energy conservation mechanisms, and they require coordinated consumption by a second partner organism for species growth. Anaerobes adapted to environmental stresses and their enzymes have biotechnological applications in organic waste treatment systems and chemical and fuel production systems based on biomass-derived substrates or syngas. These kinds of anaerobes have only recently been examined by biologists, and considerably more study is required before they are fully appreciated by science and technology.

A phospholipase A2 inhibitor decreases generation of thiobarbituric acid reactive substance during lung ischemia-reperfusion

A novel active-site directed specific inhibitor of phospholipase A2 (PLA2), 1-hexadecyl-3-trifluoroethylglycero-sn-2-phosphomethanol (MJ33), administered endotracheally co-dispersed in liposomes, significantly reduced the formation of thiobarbituric acid reactive substances (TBARS) in isolated rat lungs subjected to ischemia-reperfusion. Elevated conjugated dienes were unaffected. This contrasts with the effects of the cyclo-/lipoxygenase inhibitor 5,8,11,14-eicosatetraynoic acid (ETYA), which decreased formation of both TBARS and conjugated dienes (CD). The effects of MJ33 plus ETYA were additive for TBARS but results for CD were similar to ETYA alone. A similar dissociation of inhibition of TBARS and CD formation by MJ33 was observed with t-butyl hydroperoxide induced lipid peroxidation of isolated lung microsomes. Assay of lung homogenate with phosphatidylcholine as substrate showed that MJ33 selectively inhibited the Ca(2+)-independent acidic PLA2. MJ33 had no effect on thromboxane B2 release by the isolated lung, indicating the effects of acidic PLA2 inhibition do not involve the arachidonate cascade. MJ33 also partially prevented lung edema and lactate dehydrogenase release associated with ischemia-reperfusion. The observations show that this PLA2 inhibitor can be delivered to oxidant-sensitive lung sites by its co-dispersal in liposomes, and that oxidant-induced lipid peroxidation in this model of lung injury occurs in a complex lipid prior to PLA2 activity.