Interaction of pancreatic phospholipases A2 and semisynthetic mutants with anionic substrates and substrate analogues

Recently it was shown that porcine pancreatic phospholipase A2 aggregates in the presence of submicellar concentrations of anionic substrates [van Oort, M.G., Dijkman, R., Hille, J.D.R., & de Haas, G.H. (1985) Biochemistry 24, 7993-7999]. In the resulting complexes the enzyme displays very high catalytic activity. In this study the interaction process was further investigated by using pancreatic phospholipases A2 of different origins and several semisynthetic mutants in which one particular amino acid residue was substituted. By use of directing binding studies with a nondegradable anionic substrate analogue and monomolecular surface film kinetics on 1,2-didecanoyl-sn-glycerol 3-sulfate, it is shown that the aggregation process is controlled by the ionization state of the side chains of the amino acid residues at positions 6 and 17.