Phospholipase A2 activity on mixed lipid monolayers: Inhibition and activation of phospholipases A2 from porcine pancreas and Crotalus adamanteus by anionic and neutral amphiphiles

The effects of anionic and neutral amphiphiles on porcine pancreatic and Crotalus adamanteus phospholipases A2 were studied in a monolayer system as a function of surface pressure. The insoluble amphiphile, dicetyl phosphate (DCP), inhibited the hydrolysis of didecanoylphosphatidylcholine (DDPC) by both enzymes below their normal cutoff pressures with pure DDPC. DCP, however, enhanced enzyme penetration and thus activated the pancreatic enzyme above its normal cutoff pressure. The soluble surfactants, 3,5-dibromo- and 3,5-diiodosalicyclate, acetyl salicylate, and salicylic acid, had similar effects. 1,2-Didecanoin inhibited the hydrolysis of DDPC below the normal cutoff pressures and increased the cutoff pressures for both enzymes. Zwitterionic detergents, N-dodecyl- and N-tetradecyl-N,N-dimethyl-3-aminopropanesulfonate, were found to be potent inhibitors of the pancreatic enzyme on DDPC monolayers. Relative substrate specificities for both enzymes were determined as a function of surface pressure with phosphatidylcholine, phosphatidylglycerol, and phosphatidic acid. Pancreatic phospholipase A2 was more active and penetrated to higher pressures with the anionic phospholipids, while the venom enzyme was more active with phosphatidylcholine.