Unusual kinetic behavior of porcine pancreatic (pro)phospholipase A2 on negatively charged substrates at submicellar concentrations

Publisher Website
Google Scholar
Abstract
The negatively charged detergents S-n-alkanoylthioglycol sulfates (C8, C9 and C10) are substrates for porcine pancreatic phospholipase A2 and its zymogen. At pH 6.0 and detergent concentrations up to 0.08 .times. critical micelle concentration (cmc), the activities of active enzyme and zymogen are similar and very low. From 0.08 .times. cmc to 0.12 .times. cmc a tremendous increase in activity is observed for phospholipase A2, but not for the zymogen. Concomitant with this increase in activity there is a sharp rise in MW of the substrate-enzyme complex, from 15,000 to 95,000, and in detergent to protein molar ratio of 1:1 to .apprx. 7:1. This indicates both substrate and enzyme aggregation. Most probably a lipid-water interface is formed inside the aggregated protein particle by which the enzyme is activated. Although the zymogen also forms high MW complexes with similar molar ratios, no activation is observed probably because of distortion of its lipid binding domain.