[Phospholipase A2 of the adipocyte cytoplasmic membrane].
Explore the source record for details and available documents.
Adipose Tissue↗
Biomedical subjects
O Colard-Torquebiau
Publications and source records attributed to O Colard-Torquebiau.
Phospholipases A1 and A2 of rat liver plasma membranes; mechanism of action.
While V/S plots of phospholipase A1 show a phase transition, kinetic behaviour of phospholipase A2 acting in the same concentration range is hyperbolic. However after phospholipase A2 has been solubilized from the plasma membranes by 1 M NaCl, the V/S curve shows a phase transition. Membrane-bound phospholipase A1 shows a narrow optimum pH at 8.5 -9, while phospholipase A2 activity presents only small variations between pH 7 and 9.5. Towards exogenous phospholipids at the optimum pH 8.5 of phospholipase A1, the specific activity of the latter is 3-fold higher than phospholipase A2 specific activity. On the contrary towards endogenous phospholipids, phospolipase A2 activity is higher than phospholipase A2 activity. Moreover labeled endogenous PE hydrolysis by phospholipase A2 is decreased by addition of non labeled exogenous PE into the incubation medium. All these data suggest that the active site of phospholipase A1 is turned to the outside and acts only on exogenous substrates: for phospholipase A2 it would be inside, and exogenous phospholipids could be hydrolyzed only after penetrating the membrane.
Animals↗
[Rat liver plasma membrane phospholipase A].
The plasma membranes phospholipase A2 studied in situ shows very little sensitivity for pH variations ; the optimal concentration for Ca++ is 5 mM ; the enzymatic kinetics are of the Michaelis type. An inactive state of the phospholipase A2 exists : when rats are injected with heparin, their plasma membranes contain a very low phospholipase A2 activity. These membranes recover a high A2 activity if they are incubated in the presence of a rat platelets lysate. Treatment of membranes by NaCl 1 M displaces phospholipase A1 and phospholipase A2 but for the latter only when being in active state. Treatment of animals, conditions of preparation and of incubation of membranes influence the respective amounts of phospholipases A1 and A2 present in these membranes and are discussed in this paper. The localisation of these enzymatic proteins inside the membrane according to the membranous model proposed by Singer et al. [18] is also discussed.
Animals↗