Characterization of the interaction of phospholipase A(2) with phosphatidylcholine-phosphatidylglycerol mixed lipids

The first requirement in the hydrolysis of phospholipid bilayers by phospho lipase A(2) is the interaction of the enzyme with the bilayer surface. The catalytic ability of phospholipase A(2) has been shown to be extremely sens itive to the topology of the bilayer to which it binds and hydrolyzes. Phos pholipid bilayer properties and composition such as unsaturation, charge, a nd the presence of reaction products are known regulators of the catalytic activity of phospholipase A(2) toward the phospholipids and influences the binding of enzyme to the membrane. We show in this paper that the effect of increased anionic lipid results in enhanced binding that can be described quantitatively in terms of a simple phenomenological model. However, the in teraction with anionic lipid does not singularly dominate the thermodynamic s of binding, nor can the lag phase observed in the time course of hydrolys is of large unilamellar vesicles simply be the result of limited interactio n between the enzyme and the bilayer. Furthermore, we show that phospholipa se A(2) from Akgistrodon piscivorus piscivorus can exist in at least two bi layer-bound states and that the absence of a fluorescence change upon mixin g the enzyme with lipid bilayers does not necessarily indicate the absence of an interaction.