Effect of the state of phosphatidylcholine on the rate of its hydrolysis by phospholipase A 2 (bee venom)

Abstract

Activation of the rate of hydrolysis of egg lecithin by bee venom phospholipase is compared under a variety of substrate modification conditions, such as the presence of n -hexanol, n -propanol, Triton X-100, and deoxycholate. Experimental conditions are devised such that almost all the phospholipid in the unsonicated multilamellar liposomes can be made directly accessible to the enzyme under zero-order steady-state conditions. The kinetic results show that only in an aggregate state does lecithin serve as a substrate. Optimal activation is achieved when the additive-to-lipid ratio is more than 1:1 and less than 2:1. However, when compared under optimal conditions, different activating agents show some intrinsic differences which are reflected in the magnitude of the kinetic parameters. The results also demonstrate that a lecithin bilayer can serve as an ideal substrate for the bee venom phospholipase when the bilayer is modified by n -hexanol.