Kinetic behavior of porcine pancreatic phospholipase A2 on zwitterionic and negatively charged single-chain substrates.

The kinetic properties of porcine pancreatic phospholipase A2 were studied on a series of n-acylglycollecithins and n-acylglycol sulfates containing acyloxy or acylthio ester bonds at substrate concentrations below and above the critical micelle concentration. These single-chain detergents containing a primary (thio) ester bond are hydrolyzed rather slowly by the pancreatic enzyme, and maximal activity was found always for the n-octanoyl derivatives. The acylthio ester group is split 4-5 times faster than the corresponding acyloxy ester function. The kinetic behavior of the enzyme acting on zwitterionic glycollecithins or on anionic glycol sulfates is quite different and provides an explanation for the differences in pH optimum. Both for glycollecithins and for glycol sulfates, maximal enzyme activities are found in high molecular weight aggregates consisting of several enzyme molecules and detergent monomers. Their pathway of formation, however, is not the same.