SEARCH · PubMed Health

Results for “PHOSPHOLIPASE”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 829 records · Page 46Linked to original sources

PubMed1981

Phosphatidylinositol-specific phospholipase C in fetal membranes and uterine decidua.

An assay procedure was developed in which phosphatidyl[2-(3)H]inositol was employed as substrate for the measurement of phosphatidylinositol-specific phospholipase C activity. Employing this assay, phosphatidylinositol-specific phospholipase C activity in human fetal membranes and uterine decidua was identified and characterized. The specific activity of this enzyme in amnion (4.4 mumol x mg(-1) protein x h(-1)) was three times that in uterine decidua and more than five times that in chorion laeve. No difference was found between the specific activity of phosphatidylinositol-specific phospholipase C in placental amnion and that in reflected amnion. The products of phosphatidylinositol hydrolysis in short-term incubations were stoichiometric amounts of diacylglycerol and inositol-1,2-cyclic-phosphate plus inositol-1-phosphate. After longer periods of incubation, monoacylglycerol also was detected. Diacylglycerol lipase activity also was demonstrated in these tissues. More than 90% of phosphatidylinositol-specific phospholipase C activity of amnion tissue was recovered in the 105,000-g supernatant fraction, and optimal enzymatic activity in vitro was observed at pH 6.5-7.5 in the presence of Ca(2+) (8 mM) and mercaptoethanol (4 mM). Phosphatidylinositol-specific phospholipase C activity was stimulated by fatty acids in low concentrations, but was inhibited by lysophosphatidylcholine and a variety of detergents. No effect of labor on the specific activity of phosphatidylinositol-specific phospholipase C in either fetal membranes or uterine decidua could be detected. The finding of an active phosphatidylinositol-specific phospholipase C activity in human fetal membranes and uterine decidua is complementary to our previous finding of a selective loss of arachidonic acid from phosphatidylinositol of human fetal membranes during labor. The action of phosphatidylinositol-specific phospholipase C, coupled to diacylglycerol lipase action, could provide a mechanism for the release of arachidonic acid for prostaglandin biosynthesis during parturition.

Arachidonic Acids↗

PubMed1982

Intestinal phospholipase, a novel enzyme.

We evaluated phospholipase activity in the intestine of rats and other species. Phospholipase activity was assayed by a surface barostat technique or an egg yolk titration system. Mucosal activity was found only by the surface barostat technique with phosphatidylglycerol as substrate; it was not found with phosphatidylcholine as substrate in assays by either technique. In gut luminal fluid activity was found when both phosphatidylcholine and phosphatidylglycerol were used as substrate in assays by the surface barostat technique, and phosphatidylcholine as substrate yielded activity in egg yolk titration. In rats in which pancreatic juice had been diverted, mucosal and gut luminal phospholipase activity was greater than in controls, thus demonstrating that enzyme activity was not due to pancreatic phospholipase. Bacterial origin of phospholipase activity was excluded in that phospholipase activity was found in germ-free rats; gastric and salivary gland origins were excluded in that continued phospholipase activity was found in rats with gastric fistula. The physiological importance of the enzyme was established by the finding that rats with pancreatic fistula absorbed 111 mumol of phosphatidylcholine and that controls absorbed 119 mumol of a 135-mumol load. Activity was found to be three times greater in the distal than in the proximal intestine; in cryptal cells it was 10 times greater than in villus tip cells. 65% of the activity in the gut lumen was tightly bound to particulate matter. We propose that intestinal phospholipase may be important in gut bacterial control, in the digestion of vegetable matter (phosphatidylglycerol is a major phospholipid in both plants and bacteria), and in the digestion of phospholipids in the gut lumen.

Animals↗

PubMed1993

Isolation of a human myocardial cytosolic phospholipase A2 isoform. Fast atom bombardment mass spectroscopic and reverse-phase high pressure liquid chromatography identification of choline and ethanolamine glycerophospholipid substrates.

Recent studies have demonstrated the existence of a novel family of calcium-independent plasmalogen-selective phospholipases A2 in canine myocardium that have been implicated as enzymic mediators of ischemic membrane damage. We now report that human myocardium contains two functionally distinct isoforms of cytosolic calcium-independent phospholipase A2. The major cytosolic phospholipase A2 isoform preferentially hydrolyzes plasmalogen substrate, possesses a pH optimum of 7.0, and is chromatographically resolvable from a minor cytosolic calcium-independent phospholipase A2 isoform that hydrolyzes plasmenylcholine and phosphatidylcholine substrates at similar rates and possesses a pH optimum of 8.5. The major cytosolic calcium-independent phospholipase A2 isoform was identified as a 40-kD polypeptide after its 182,000-fold purification by sequential column chromatographies to a final specific activity of 67 mumol/mg.min. The purified 40-kD human myocardial phospholipase A2 preferentially hydrolyzes plasmalogens containing arachidonic acid at the sn-2 position. Both reverse-phase HPLC and fast atom bombardment mass spectroscopic analysis of human myocardial ethanolamine and choline glycerophospholipids demonstrated that plasmenylethanolamine and plasmenylcholine molecular species containing arachidonic acid at the sn-2 position are prominent constituents of human myocardium. Collectively, these results identify and characterize the major human myocardial cytosolic calcium-independent phospholipase A2 activity, demonstrate the presence of functionally distinct human myocardial cytosolic calcium-independent phospholipase A2 isoforms, and document the abundance of arachidonoylated plasmalogen molecular species in human myocardium that serve as substrates.

Arachidonic Acid↗

PubMedDate not supplied

Inhibited serum phospholipase A2 activity in hyperbilirubinemia.

BACKGROUND/AIMS: Phospholipase A2 activity is reported to be related to the physiology of various disorders, and the activity is modified by deoxycholic acid. METHODOLOGY: Serum phospholipase A2 activity was measured by counting the radioactivity of 14C-palmitic acid released from L-3-phosphatidylcholine (1-palmitoyl-2-14C-palmitoyl) in 40 patients with hyperbilirubinemia due to malignant neoplasms and benign cholestasis. Phospholipase A2 activity in serum from healthy subjects was also measured after incubation with 5-30 mg of bilirubin per dL or 0.1-5 mM of cholic acid for 60 min at 37 degrees C. RESULTS: Serum phospholipase A2 activity was significantly lower in patients with hyperbilirubinemia. There were negative correlations between serum phospholipase A2 activity and concentration of total bilirubin (r = 0.668; P < 0.0001) or total bile acids (r = 0.423; P < 0.05) in patients with hyperbilirubinemia. In 12 patients who underwent percutaneous transhepatic biliary drainage, the low serum phospholipase A2 activity was reversed while bilirubin concentrations decreased. Incubation of sera from healthy subjects with more than 3 mM cholic acid significantly reduced phospholipase A2 activity (P < 0.01), whereas incubation with bilirubin had no effect. CONCLUSIONS: Inhibition of serum phospholipase A2 activity in patients with hyperbilirubinemia may be caused by increased serum cholic acid concentration.

Adult↗

PubMed1992

Interleukin-1 beta- and forskolin-induced synthesis and secretion of group II phospholipase A2 and prostaglandin E2 in rat mesangial cells is prevented by transforming growth factor-beta 2.

Interleukin-1 beta and forskolin induce prostaglandin E2 release as well as 14-kDa group II phospholipase A2 gene expression and secretion of the enzyme from rat glomerular mesangial cells. We now report that pretreatment of mesangial cells with transforming growth factor-beta 2 prior to stimulation with interleukin-1 beta or forskolin inhibits the induced release of prostaglandin E2. At the same time the secretion of group II phospholipase A2, measured both as enzyme activity with sn-2-labeled phosphatidylethanolamine as substrate and as enzyme protein in immunoblot experiments, is dose-dependently inhibited by pretreatment of the cells with transforming growth factor-beta 2. Analyses of enzyme activity and enzyme protein levels in the cells indicated that this is not due to inhibition of enzyme secretion with a concomitant increase in cellular levels of the enzyme. Rather, pretreatment of the cells with transforming growth factor-beta 2 largely prevented both the interleukin-1 beta- and the forskolin-induced synthesis of phospholipase A2. This is the first report indicating an inhibition of group II phospholipase A2 gene expression by transforming growth factor-beta 2. In line with those results, transforming growth factor-beta 2 did not induce the synthesis and secretion of group II phospholipase A2. However, under conditions where the interleukin-1 beta-induced expression of group II phospholipase A2 is fully suppressed by transforming growth factor-beta 2, the growth factor itself stimulated prostaglandin E2 synthesis by a mechanism apparently not involving group II phospholipase A2. The immunochemical identification of the inducible and secretable phospholipase A2 from rat mesangial cells as a group II enzyme was confirmed by purification and N-terminal amino acid sequence determination.

Amino Acid Sequence↗

PubMed1996

Myocardial calcium-independent phospholipase A2 activity during global ischemia in isolated rabbit hearts.

OBJECTIVES: To study calcium-independent phospholipase A2 activity during global ischemia in isolated rabbit hearts by measuring the hydrolysis of the endogenous choline phospholipids. METHODS: Langendorff perfused rabbit hearts were exposed to global ischemia for 15 or 60 min, or control perfusion for the same length of time. The hearts were then rapidly frozen in liquid nitrogen and lyophilized. Calcium-independent phospholipase A2 activity in the lyophilized tissue was studied by measuring accumulation of lysophospholipids resulting from hydrolysis of both the choline diacylphospholipid and the choline plasmalogen pool. RESULTS: The calcium-independent phospholipase A2 activity showed the same pH, temperature and calcium sensitivity in control and ischemic (15 min of ischemia) lyophilized myocardial tissue. Incubation of control and ischemic tissue showed no difference in the rate of accumulation of lysophospholipids when the ischemic tissue was obtained from hearts exposed to 15 min of ischemia (107 +/- 4 vs 111 +/- 7 nmol/g dry wt x min, ischemia versus control, mean +/- s.e.m., n = 8), but a significant decrease was noticed in tissue from hearts that had been exposed to 60 min of ischemia (31 +/- 9 vs 86 +/- 18 nmol/g dry wt x min, P < 0.05, n = 4). The decreased phospholipase A2 activity in tissue exposed to 60 min of ischemia was not due to enhanced metabolism of the lysophospholipids (84 +/- 15 vs 79 +/- 8 nmol/g dry wt x min, n = 4). The calcium-independent phospholipase A2 activity was considerably lower in fresh myocardial tissue compared with lyophilized tissue, but comparison of control and ischemic fresh tissue gave results comparable to those found using lyophilized tissue. The myocardial calcium-independent phospholipase A2 activity showed no plasmalogen selectivity in either control or ischemic myocardium. CONCLUSIONS: In isolated perfused rabbit hearts we found no evidence for activation of calcium-independent phospholipase A2 activity during global ischemia. With prolonged time of ischemia there was a significant decrease in calcium-independent phospholipase A2 activity.

Animals↗

PubMedDate not supplied

[Effect of phospholipase A2 on H+-ATPase in the plasma membrane of H+-ATPase in maize root cells].

The plasma membrane H(+)-ATPase which plays a central role in plant cell physiology is lipid-dependent enzyme. Lipid composition of plasma membrane can be modified by the action of endogenous phospholipases. Recently it has been supposed that the plasma membrane phospholipase A2 participates in phytohormonal signal transduction on the H(+)-ATPase protein. We have investigated the effect of phospholipase A2 on the H+ ATPase activity in plasma membrane preparations isolated from 7-days corn seedling roots. The exogenous phospholipase A2 from snake venom and lipid hydrolysis products of the phospholipase A2-catalysed reaction have been used. It was found that the phospholipase A2 increased plasma membrane H(+)-ATPase activity during first 15 sec. but inhibited it under the longer exposition. Examination of lyso-derivatives effect on plasma membrane preparations demonstrated a 2-3-fold increasing of their H(+)-ATPase activity by lysophosphatidylcholine whereas the effect of lysophosphatidic acid was expressed to higher extent. Studying of the effects of unsaturated free fatty acids as the second hydrolysis product has shown that linolic and linolenic acids activated the plasma membrane H(+)-ATPase at concentration of 10 microM but inhibited it at higher concentrations. Exposition of plasma membranes with the phospholipase A2 or fatty acids shifted H(+)-ATPase pH optimum from pH 6.5 to pH 7.0. The role of endogenous phospholipase A2 in regulation of plasma membrane H(+)-ATPase activity has been under discussion.

Cell Membrane↗

PubMed1998

Bacterial phospholipases.

The phospholipases are a diverse group of enzymes, produced by a variety of Gram-positive and Gram-negative bacteria. The roles of these enzymes in the pathogenesis of infectious disease is equally diverse. It is only recently that molecular genetic approaches have allowed data to be obtained which indicates the role of these enzymes in the disease process. In the case of some pathogens phospholipases play an overriding role in disease. Roles for these enzymes have been demonstrated in the pathogenesis of disease caused by extracellular and intracellular pathogens and by disease caused by pathogens which enter via the respiratory tract, the intestinal tract or after traumatic injury. Some of the mechanisms by which phospholipases C affect tissues in vitro or ex vivo are understood but, in the main, the mechanisms by which phospholipases C affect tissues in vivo are not known. A key event, which can determine the extent of involvement of phospholipases in the disease process, is the interaction of the enzyme with phospholipids in eukaryotic cell membranes. Whilst progress has been made in understanding the molecular basis of these interactions, the process is far from understood. Two theories attempt to explain the reasons why only some phospholipases C are membrane active. In general, the membrane active enzymes are able to hydrolyse both phosphatidylcholine and sphingomyelin and appear to have mechanisms which allow them to interact with membrane phospholipids. The structural differences between phosphatidylcholine and sphingomyelin lie within the fatty acyl chain/ester bond region which would be partially embedded in the membrane bilayer. Therefore, there may be a common explanation for membrane interaction and recognition of both phospholipid types. The value of this information will be several fold. The demonstration of the role of these enzymes in disease will allow the development of vaccines or therapeutics which block the effects of these enzymes. In this context it is worth bearing in mind that eukaryotic phospholipases C, which play key roles in many inflammatory and autoimmune diseases, are the subject of intense study by the pharmaceutical industry. Some of the bacterial toxins are potent cytotoxic agents and this has encouraged some workers to explore the possibility that immunotoxins can be developed (Chovnick et al. 1991). Purified recombinant phospholipases C will continue to be used in the study of cell membranes, and the increasing numbers of enzymes with different substrate specificities will enhance their application.

Bacteria↗

PubMed1982

Effects of divalent cations, trypsin, and phospholipases on the passive permeability to sodium of inside-out vesicles from human red cells.

Inside-out vesicles (IOV) were prepared from human red blood cells. Steady-state uptake of 23Na was observed to generally follow an exponential time course with a rate constant of 1.57 +/- 0.09 h-1 (SE). One week of cold storage (0-4 degrees C) increased the rate constant to 2.50 +/- 0.12 h-1 (SE). Mg2+, Ca2+, or Sr2+ decreased the rate of 22Na uptake with no observable differences between the three divalent cations when tested at concentrations of 50 microM. Mg2+ was shown to decrease the rate of 22Na uptake at concentrations as low as 5 microM with maximal effect at 50 to 100 microM. The decrease in rate of 22Na uptake induced by Mg2+ could be enhanced by exposure of IOV to Mg2+ for longer periods of time. Trypsin treatment of OIV increased the rate of uptake of 22Na and was dependent on the concentration of trypsin added between 5 to 25 micrograms/ml (treated for 5 min at 25 degrees C). The ability of Mg2+ (50 microM) to decrease the rate of 22Na uptake was still observed after maximal trypsin treatment. Phospholipase A2 or phospholipase C treatment of IOV increased the rate of 22Na uptake and was dependent on the amount of phospholipase A2 (0.1 to 1.0 units/ml) or phospholipase C (0.25 to 2.5 units/ml) added (treated for 5 min at 25 degrees C). After phospholipase A2 treatment, the observed decrease in the rate of 22Na uptake induced by Mg2+ (50 microM) was generally greater than controls. After phospholipase C treatment, the observed decrease in rate of 22Na uptake induced by Mg2+ (50 microM) was less or absent when compared with controls. Phospholipase C treatment was less effective in preventing the Mg2+ effect the longer IOV were exposed to Mg2+. The results suggest that Mg2+ binds to phospholipid headgroups to reduce Na permeability perhaps by inducing a change in bilayer structure or phospholipid association.

Cations, Divalent↗

PubMed1980

Transbilayer distribution of phospholipids in photoreceptor membrane studied with various phospholipases.

The distribution of the three major phospholipids of bovine rod outer segment disk membranes over the two faces of the membrane has been studied by means of treatment with phospholipase C, phospholipase A2 and phospholipase D. Two different preparations of rod outer segment disk membranes have been used, which are called 'stacked disks' and 'disk vesicles' on account of their morphological appearance. The hydrolysis patterns obtained by phospholipase treatment of these preparations have been compared to those of a retinal lipid suspension or detergent-solubilized disk membranes, which serve as control preparations with a similar phospholipid composition but a random availability of the phospholipids. Special attention is given to the early phase of enzyme treatment in order to eliminate secondary effects on the molecular organization of the membrane due to appreciable phospholipid hydrolysis. Analysis of the hydrolysis patterns for all three phospholipases in stacked disks, as compared to those in randomized control preparations, suggests a slightly asymmetrical distribution of phosphatidylcholine (40--45% at the outer face) and phosphatidylethanolamine (55--60% at the outer face) and a symmetrical distribution of phosphatidylserine in rod outer segment disk membranes. Extensive treatment with phospholipases C and A2 leads ultimately to nearly complete hydrolysis of all phospholipids, but with phospholipase D a final level of 40% phospholipid hydrolysis is observed in stacked disk preparations. This suggests that in the latter case the inner face of the membrane is inaccessible to the enzyme. Further work will be necessary in order to substantiate these conclusions.

Animals↗

PubMed1983

Surface-active phospholipase A2 in mouse spermatozoa.

The partial characterization of a calcium-dependent phospholipase A2 associated with membranes of mouse sperm is described. Intact and sonicated sperm had comparable phospholipase A2 activity which was maximal at pH 8.0 using [1-14C]oleate-labeled autoclaved Escherichia coli or 1-[1-14C]stearoyl-2-acyl-3-sn-glycerophosphorylethanolamine as substrates. More than 90% of the activity was sedimented when the sperm sonicate was centrifuged at 100 000 X g, indicating that the enzyme is almost totally membrane-associated. The activity is stimulated 200% during the ionophore-induced acrosome reaction and is almost equally distributed between plasma/outer acrosomal and inner acrosomal membrane fractions. The membrane-associated phospholipase A2 had an absolute requirement for low concentrations of Ca2+; Sr2+, Mg2+ and other divalent and monovalent cations would not substitute for Ca2+. In the presence of optimal Ca2+, zinc and gold ions inhibited the activity while Cu2+ and Cd2+ were without effect. Incubation of sperm sonicates with 1-[1-14C]stearoyl-2-acyl-3-sn-glycerophosphorylethanolamine in the presence and absence of sodium deoxycholate demonstrated the presence of phospholipase A2 and lysophospholipase activities. No phospholipase A1 activity was detectable. Indomethacin, sodium meclofenamate and mepacrine, but not dexamethasone or aspirin, inhibited the sperm phospholipase A2 activity. Preincubation with p-bromophenacyl bromide inhibited phospholipase A2, suggesting the presence of histidine at the active site. The enzyme may play an important role in the membrane fusion events in fertilization.

Acetophenones↗

PubMed1986

Antigenic relatedness between human lecithin-cholesterol acyltransferase and phospholipases of the A2 family.

A monoclonal antibody, B10, generated against pure human lecithin-cholesterol acyltransferase (EC 2.3.1.43) caused the inhibition of the esterolytic and cholesterol esterifying activities of the enzyme. This antibody also reacted with a number of pancreatic and snake venom phospholipases A2 species but not phospholipase A1. A concentration-dependent inhibition of phospholipase A2 was also seen in the presence of B10. Treatment of lecithin-cholesterol acyltransferase or B10-reacting phospholipases with phenacyl bromide, a reagent known to interact with the active site of phospholipase A2, inhibited both their esterolytic activity and their capacity to bind to B10. A dimeric phospholipase A2 species with a known occluded active site did not cross-react with B10. Thus, lecithin-cholesterol acyltransferase and some enzymes of the phospholipase A2 family share a common antigenic determinant which is probably located near or at their esterolytic active site.

Animals↗

PubMed1986

Glucose transport into human erythrocytes treated with phospholipase A2 or C.

Phospholipase A2 induced crenation of human erythrocytes and decreased glucose transport activity (influx rate) by 40% when 51% of phosphatidylcholine (PC) in the membrane was hydrolyzed. On the other hand, phospholipase C induced invagination of the cells and negligibly affected the glucose transport in the case of 21% hydrolysis of the PC. By altering the pH of the medium for suspending cells treated with phospholipase A2 from 7.4 to 6.0, cell shape was changed from clear crenation to slight invagination, but glucose transport activity was not affected. Cells that were treated with phospholipase A2 and then washed with albumin to remove free fatty acids produced in the cell membrane showed an almost normal cell shape and slightly higher glucose transport activity than did untreated cells. The ratios of beta-D-glucose transport rate to alpha-D-glucose transport rate in untreated cells, cells treated with phospholipase A2 and cells treated with phospholipase C were 1.13, 1.04, and 1.20, respectively. These results demonstrate that the drastic morphological change (invagination or crenation) induced by the treatment with phospholipases bears no clear relationship to the activity of glucose transport and suggest that the increase in the volume of the outer half of the lipid bilayer might reduce the rate of glucose transport across the human erythrocyte membrane and change the anomeric preference of glucose transport.

Biological Transport↗

PubMed1982

Subcellular distribution and some properties of acid phospholipase A1 in rat testis.

The activity of phospholipase A was studied in homogenates, and mitochondria and lysosome-enriched fractions of rat testis. Using testicular homogenates and Triton X-100, phospholipase A1 activity with pH optima at 3.0 and 7.0 and phospholipase A2 activity with a pH optimum at 6.5 were observed. With optimum pH at 3.0, phospholipase A1 was further studied, identified and characterized by using 1-acyl-2-[1-(14)C]1 oleoyl-sn-glycero-3-phosphocholine as substrate in mitochondria and lysosome-enriched fractions. Acid phospholipase A1 activity was inhibited by Ca2+ and EDTA. The enzyme activity was greatly stimulated by Triton X-100, not inhibited by sulfhydryl reagents and DIFP, and relatively heat stable at 65 degrees C. Acid phospholipase A1 activity had properties similar to other phospholipases of lysosomal origin: subcellular distribution, metal independence and acid pH optimum and was mainly localized in mitochondria and lysosome-enriched fraction suggesting a lysosomal origin.

Animals↗

PubMed1999

Characterization of phospholipase A1, A2, C activity in Ureaplasma urealyticum membranes.

The presence of endogenous phospholipase A (PL-A) activity of U. urealyticum hydrolyzing the acyl ester bond and phospholipase C (PL-C) activity hydrolyzing the phosphodiester bond is primarily localized in the membranes of ureaplasmas. Characterization of the membrane PL-A and PL-C activity in exponential growing cells of serovars 3, 4, and 8 was investigated. The pH optimum was about 8.5-9 for phospholipase A1 (PL-A1) in the three serovars. A more acidic pH optimum of 6 was observed for phospholipase A2 (PL-A2) enzymes in serovars 3 and 4. However, a very significant stimulation of PL-A2 activity in serovar 8 occurred around pH 7. The specific activity of PL-A2 was always 50-100 fold higher than PL-A1 activity in the pH range studied. Ca2+ ions only slightly stimulated PL-A1 activity in all 3 serovars. PL-A1 activity was stimulated about 6-fold from 0.5-0.8 mM Ca2+ ion concentrations for serovar 3 and 12-fold for serovar 8. Only lower concentrations (0.2-0.4 mM) of calcium stimulated PL-A2 activity in serovar 4. EDTA inhibition corresponded to Ca2+ stimulation for PL-A1 activity for serovars 3 and 8. A general stimulation of PL-A1 activity by diethyl ether was evident but the degree of stimulation varied with the serovar. Sodium deoxycholate enhanced PL-A activity of serovars 4 and 3, but partially inhibited that of serovar 8. PL-A activity in the three serovars were not significantly affected by p-hydroxymercuribenzoate, a marker of -SH groups in the enzyme. All 3 serovars were inactivated by heat. A broad pH optimum for PL-C activity was evident around 7-8. Diethyl ether enhanced PL-C activity of serovar 8. Sodium deoxycholate and heat were inhibitory to PL-C activity. The results demonstrate that the major characteristics of ureaplasma membrane bound PL-A and PL-C are basically similar to those of other mollicutes and bacteria. However, the major differences in the specific characteristics of specially PL-A1 and PL-A2 suggest that the ureaplasma phospholipases are unique enzymes different from the phospholipases of bacteria. Both the PL-A and PL-C enzymes function over the broad range at which ureaplasma can grow, pH 5-9 essential for survival. The ureaplasma PL-As are also markedly different from one serovar to another. This variation in specific activity could contribute significantly to differences in virulence among serovars in specific host milieus. There is significant variation from acidic pH of the vagina and alveolar surface of the lung to a more neutral pH of the endometrium and placenta. There are marked differences in calcium concentrations under specific circumstances in various host tissues. Thus the differences in specific activity among the phospholipases of the serovars of U. urealyticum may be of physiological importance in interactions with host tissues and pathogenesis of disease.

Calcium↗

PubMed1983

Exogenous phospholipase enzymes mimic effects of phenylephrine on Ca2+ transport in hepatocytes.

Phospholipase C from Clostridium perfringens induced the release of 45Ca2+ from isolated rat hepatocytes incubated at 0.1 mM extracellular Ca2+ with a time course similar to that for the action of phenylephrine. Under the conditions of these experiments, no significant damage to the plasma membrane was detected in the presence of phospholipase C. Little 45Ca2+ release was induced by bee venom phospholipase A2. At 1.3 mM extracellular Ca2+, both phospholipase enzymes stimulated the initial rate of 45Ca2+ exchange. Concentrations of phospholipase C comparable with those that stimulated 45Ca2+ release increased the rates of glucose release and O2 utilization by 70 and 20% respectively. An increase in the rate of O2 utilization but not glucose release was observed after the addition of phospholipase A2 to hepatocytes. The possible role for a cellular phospholipase C in the mechanism by which phenylephrine stimulates glycogenolysis in the liver cell is briefly discussed.

Animals↗

PubMed1982

Topological location and biological significance of phospholipids in the membrane of Newcastle disease virus. Hydrolysis of phospholipids in intact virion with pure phospholipases A2, C, and D.

The composition, topological distribution and biological significance of phospholipids in the membrane of Newcastle disease virus (NDV) grown in embryonated chicken eggs were investigated. Phosphatidylethanolamine and sphingomyelin were the predominant phospholipids in NDV membrane. The location of phospholipids in the lipid bilayer of the membrane was studied by assessing their reactivities with highly purified phospholipase A2 (Agkistrodon halys blomhoffi) and phospholipase D (Streptomyces chromofuscus), and the biological role of membrane phospholipids was also investigated by using pure phospholipases A2, C (Bacillus cereus) and D. Choline-containing phospholipids were found predominantly in the outer layer of the membrane. The inner layer was composed mainly of aminoglycerophospholipids, though a fair amount of them also appeared to be located in the outer half of the bilayer. When intact virion was treated with phospholipase C, marked decreases in hemolytic activity and infectivity mediated by viral fusion (F) glycoprotein were observed, but hemagglutinating and neuraminidase activities did not change significantly. Apparently complete hydrolysis of phospholipids in the outer half of the lipid bilayer with phospholipase D caused about 22% decrease in the original hemolytic activity. On the other hand, when all phosphatidylcholine and aminoglycerophospholipids in the outer half of the viral membrane were hydrolyzed with purified phospholipase A2, no significant change in viral hemolytic activity or morphology was detected. No marked change of hemagglutinating and neuraminidase activities was detected on treatment of NDV with phospholipases A2 and D. The above results suggest that the integrity of fatty acid ester of glycerophospholipids in NDV membrane is not essential for the manifestation of viral activities, though polar groups of the phospholipids in the outer half of the membrane may be involved in the function of fusion (F) glycoprotein, but not in that of hemagglutinating and neuraminidase (HN) glycoprotein of NDV.

Hydrolysis↗

PubMed1988

Phospholipases modulate the rat testicular androgen biosynthetic pathway in vitro.

The role of membrane phospholipids in testicular androgen biosynthesis was investigated by monitoring the effects of phospholipase treatments on the activities of the steroid transforming enzymes. Androgen biosynthesis in untreated rat testicular microsomes was examined by monitoring the temporal appearance of pregnenolone metabolites and was found to proceed through the 4-ene route. When phospholipase A2 was included, the 5-ene steroids 17-hydroxypregnenolone and dehydroepiandrosterone (DHEA) were formed in greater quantities, and the production of 4-ene steroids was reduced indicating that the conversion of 5-ene steroids to the 4-ene configuration was inhibited by phospholipase A2 treatment. Phospholipase C, in addition to inhibiting this step, also inhibited the conversion of C21 steroids to C19 steroids. When the enzymatic steps were measured individually, phospholipase A2 inhibited 3 beta-hydroxysteroid dehydrogenase-isomerase (3 beta-HSD-Isomerase) with an ED50 of 73 mU/ml but had no effect on the activities of 17-hydroxylase, C-17, 20 lyase, or 17 beta-hydroxysteroid dehydrogenase (17 beta-HSD). However, though phospholipase C treatment inhibited 3 beta-HSD-Isomerase, it caused less inhibition (the ED50 value was 149 mU/ml). Furthermore, 17-hydroxylase and C-17, 20 lyase activities were also inhibited by phospholipase C treatment (ED50 values were 410 and 343 mU/ml, respectively), but no effect on 17 beta-HSD was observed. The differences in the apparent phospholipid requirements of the steroidogenic enzymes provides the possibility that the metabolic fate of pregnenolone may be regulated by changes in the phospholipid composition of the microenvironment.

17-Hydroxysteroid Dehydrogenases↗