Spontaneous phospholipase A activity of rat pancreatic homogenates]

Rat pancreas presents a spontaneous phospholipase A activity which appears before trypsin activation at optimal pH 6.5. The responsible enzyme is independent of pancreatic prophospholipase A, as can be seen through experiments done in the presence of trypsin inhibitors. On the other hand, this enzyme is distinct from excretory phospholipase which is more active and whose optimal pH is 8.8. Thermostability and insensibility of spontaneously active phospholipase A to DFP differentiate it from lipase, carboxyl-esterhydrolase and lysophospholipase, respectively.     

Activity of phospholipases A and some lysosomal enzymes in rat testes at different stages of hypervitaminosis A

Summary Excess of vitamin A induces decrease of neutral phospholipase A₁ and A₂ activity in rat testes homogenates on the 4th day, and increase of -galactosidase activity on the 8th day of treatment. It is suggested that phospholipase A activity decrease is of great importance in development of testicular disorders, caused by disbalance of vitamin A.     

The generation and identification of the hemolysin of Trypanosoma congolense

Summary The hemolytic activity of Trypanosoma congolense appears to be due to the presence of free fatty acids generated by the action of phospholipase A on endogenous phosphatidyl choline. Some lysolecithin also contributes to the lytic activity. Trypanosoma lewisi, being devoid of phospholipase A does not generate free fatty acids and is therefore non-hemolytic.This research was supported by the International Development Research Center.     

Role of phospholipids in the binding activity of vasoactive intestinal peptide receptors

Phospholipase digestion of rat intestinal epithelial cell membranes was performed in order to study the influence of membrane phospholipids on the binding activity of VIP receptors. Phospholipases A2 and C strongly (ED50 congruent to 4 X 10(-2) and 4 X 10(-1) micrograms/ml, respectively) and rapidly reduced 125I-VIP binding to membranes whereas phospholipase D was ineffective. This suggests an important role of both hydrophobic and hydrophilic groups of phospholipids on VIP receptor binding activity.     

Possible regulation of membrane-associated cyclic AMP phosphodiesterase in rat cerebral cortex by lipids.

Cyclic AMP phosphodiesterase (PDE) in membrane fraction from rat cerebral cortex was activated by Triton X-100, and treatment at alkaline pH and with phospholipase C. These results suggest that membrane PDE exists in a latent form and is influenced by microenvironmental changes within the membrane. Furthermore, the PDE, unlike soluble enzyme, is not influenced by a protein activator and Ca++.     

Multiple phospholipase activation by OX1 orexin/hypocretin receptors

We investigated coupling of OX(1) receptors to phospholipase activation and diacylglycerol generation in Chinese hamster ovary (CHO) cells using both biochemical and fluorescence "real-time" methods. The results indicate that at lowest orexin-A concentrations (highest potency), diacylglycerol generated results from phospholipase D activity. At 10-100-fold higher orexin-A concentrations, phospholipase C is activated, likely hydrolyzing phosphatidylinositol (PI) or phosphatidylinositol monophosphate (PIP) but not phosphatidylinositol bisphosphate (PIP(2)). At further 7-fold higher orexin-A concentrations, PIP(2) is hydrolyzed, releasing both diacylglycerol and inositol-1,4,5-trisphosphate. Thus, OX(1) orexin receptors connect to multiple phospholipase activities, apparently composed of at least one phospholipase D and two different phospholipase C activities. At low agonist concentrations, diacylglycerol and phosphatidic acid are the preferred products, and interestingly, it seems that even the primarily activated phospholipase C mainly works to increase diacylglycerol and not inositol-1,4,5-trisphosphate.     

Lipase activity of anaerobic bacteria on glycerol-tributyrate determined by gas-liquid chromatography]

Anaerobic bacteria are classified among other criteria by the presence or absence of phospholipase and lipase. The liquid gas chromatographic method detects with great sensibility the lipasic activity of the anaerobic bacteria. A liidolytic action has been demonstrated in Cl. perfringens.     

Possible regulation of membrane-associated cyclic AMP phosphodiesterase in rat cerebral cortex by lipids

Summary Cyclic AMP phosphodiesterase (PDE) in membrane fraction from rat cerebral cortex was activated by Triton X-100, and treatment at alkaline pH and with phospholipase C. These results suggest that membrane PDE exists in a latent form and is influenced by microenvironmental changes within the membrane. Furthermore, the PDE, unlike soluble enzyme, is not influenced by a protein activator and Ca⁺⁺.     

Malignant hyperthermia: molecular defects in membrane permeability

Malignant hyperthermia (MH), a genetically inherited disorder of skeletal muscle, is due to molecular defect in membrane permeability. The alteration in membrane permeability is suggested to be due to enhanced phospholipase A2 activity which is responsible for the increased level in sarcoplasmic Ca2+. The excess Ca2+ is responsible for muscle hyper-rigidity and enhanced rate of glycolysis, resulting in a rapid rate of lactic acid production and a low pH in MH muscle.     

Direct measurement of the pH in the stomach of the conscious rat, using a special electrode.

The construction and use of a specially designed electrode to measure gastric pH in the conscious rat is described. Measurement of gastric hydrogen ion activity with this device is rapid and reproducible in starved rats. A dose-related increase of gastric pH was obtained after s.c. injection of the anticholinergic isopropamide.     

Serienbestimmung der Phospholipase-A-Aktivität in chromatographischen Fraktionen

Summary A simple assay is described for phospholipase A in chromatographic fractions. 0.01 ml of the fraction is added to 1 ml of a 1% solution of purified lecithin in ether (100 vol) — picoline (10 vol) — 4.5 mmol CaCl₂ (1 vol). The presence of phospholipase A is indicated by the appearance of a turbidity due to precipitation of lysolecithin. The lag period until precipitation occurs gives an indication of the relative concentration of enzyme present.     

Direct measurement of the pH in the stomach of the conscious rat,using a special electrode

Summary The construction and use of a specially designed electrode to measure gastric pH in the conscious rat is described. Measurement of gastric hydrogen ion activity with this device is rapid and reproducible in starved rats. A doserelated increase of gastric pH was obtained after s.c. injection of the anticholinergic isopropamide.Acknowledgment. We wish to thank Mr F. Lenaerts and Mr J. Vermeire for careful assistance in these studies.     

Modulation of phospholipase A2 activity generated by molecular evolution

Snake venom oligomeric neurotoxins offer several unique examples of modulation of phospholipase A2 (PLA2) activity generated by molecular evolution. This phenomenon was found in evolutionary younger snakes and is probably common for representatives of the genus Vipera. At present, the best-studied example is the heterodimeric neurotoxin vipoxin from the venom of the southeast European snake Vipera ammodytes meridionalis. It is a complex between a basic strongly toxic PLA2 and an acidic and catalytically inactive PLA2-like component (Inh). This is the first reported example of a high degree of structural homology (62%) between an enzyme and its natural protein inhibitor. The inhibitor is a product of the divergent evolution of the unstable PLA2 in order to stabilize it and to preserve the pharmacological activity/toxicity for a long time. Inh reduces both the catalytic activity and toxicity of PLA2. Vipoxin also illustrates evolution of the catalytic into a inhibitory function. Vipoxin analogues have been found in the venom of viperid snakes inhabiting diverse regions of the world. An attempt is made to explain modulation of the toxic function by the three-dimensional structure of vipoxin.     

DOCA administration increases renal phospholipase activity in the rat

Summary The phospholipase activity of renal tissue has been evaluated in controls and in DOCA treated rats. DOCA treated animal showed a higher than normal enzyme activity. Since a phospholipase is the key step in prostaglandin biosynthesis, it is suggested that the increased prostaglandin release promoted by mineraloactive steroids is mediated by an activation of this key enzyme.This work has been partly supported by a grant from Consiglio Nazionale delle Ricerche.To whom reprint requests should be addressed.     

Microbiology of subteranean waste sites

Summary Excavated repositories for radioactive waste in deep and shallow geological formations will be subject to microbial contamination; therefore, a number of groundwater environments have been examined in Europe for the presence and activity of microorganisms. Common soil bacterial isolates were found to predominate in the groundwaters. Their activity is curtailed by the oligotrophic conditions encountered. It still remains to be demonstrated whether waste and waste isolation materials such as cellulose and bitumen will provide an exogenous nutrient source for the microorganisms and whether microbial activity will compromise nuclear waste immobilisation. A further constraint to the microorganisms is the high pH near-field environment generated by cement/concrete barriers.     

Malignant hyperthermia: Molecular defects in membrane permeability

Summary Malignant hyperthermia (MH), a genetically inherited disorder of skeletal muscle, is due to molecular defect in membrane permeability. The alteration in membrane permeability is suggested to be due to enhanced phospholipase A₂ activity which is responsible for the increased level in sarcoplasmic Ca²⁺. The excess Ca²⁺ is responsible for muscle hyper-rigidity and enhanced rate of glycolysis, resulting in a rapid rate of lactic acid production and a low pH in MH muscle.     

Activity of two components of serum ribonuclease under conditions of physical exercise.

Serum ribonuclease activity before and after physical exercise in healthy persons was estimated. It is found that a work load of 6000 kgm/5 min increased ribonuclease activity measured at pH 8.5 and decreased the activity of the same enzyme measured at pH 7.0 in the presence of Zn SO4. The observed changes were more pronounced in untrained than in trained persons.     

Abtrennung des anaphylatoxinbildenden Prinzips aus Cobragift von anderen Giftkomponenten

Summary Cobra venom contains an anaphylatoxin-forming principle. This component has been purified by gel filtration and ion exchange chromatography. It has been obtained free from proteolytic or hemolytic activity as well as from phospholipase A. It seems to be an enzyme that splits the anaphylatoxin from its inactive precursor.     

Activity of two components of serum ribonuclease under conditions of physical exercise

Summary Serum ribonuclease activity before and after physical exercise in healthy persons was estimated. It is found that a work load of 6000 kgm/5 min increased ribonuclease activity measured at pH 8.5 and decreased the activity of the same enzyme measured at pH 7.0 in the presence of ZnSO₄. The observed changes were more pronounced in untrained than in trained persons.     

Failure of calcium to stimulate Na,K-ATPase in the presence of EDTA

The effect of calcium on Na,K-ATPase activity of rat brain homogenates and its modification by the chelating agent EDTA has been investigated. In the absence of EDTA, free calcium (approximately 10(-6) mol/l) stimulates Na,K-ATPase activity; in the presence of EDTA the same concentration of free calcium is without effect on the enzyme. In the absence of EDTA the stimulation by calcium of Na,K-ATPase activity is enhanced by the additional presence of calmodulin but in the presence of EDTA, even when calmodulin is added to excess, calcium still fails to stimulate the enzyme. The possibility that EDTA interferes with an interaction between a calcium-calmodulin complex and Na,K-ATPase is discussed.