Beschreibung:
<jats:p>Phospholipase A<jats:sub>2</jats:sub> (PLA<jats:sub>2</jats:sub>)‐mediated hydrolysis of membrane phospholipids was measured by ellipsometry, and the inhibition of this process by annexin V was studied. Planar membranes, consisting of phosphatidylcholine, phosphatidylethanolamine, and phosphatidylserine (PC/PE/PS; 54:33:13, on molar basis), were degraded by pancreatic PLA<jats:sub>2</jats:sub>, and the rate of hydrolysis was limited to about 0.7%/min. The influence of graded coverage of the membrane with annexin V was studied. The degree of PLA<jats:sub>2</jats:sub> inhibition was nonlinearly related to the amount of membrane‐bound annexin V, and binding of only 12% and 54% of full membrane coverage resulted in, respectively, 50% and 93% inhibition. These findings indicate that the inhibition of PLA<jats:sub>2</jats:sub>‐mediated hydrolysis by annexin V cannot be simply explained by shielding of phospholipid substrates from the enzyme. Moreover, the present results leave room for a role of endogenous annexin V in regulating phospholipid turnover in the plasma membrane of parenchymal cells such as cardiomyocytes.</jats:p>