A model for the molecular mechanism of interfacial activation of phospholipase A2 supporting the substrate theory

摘要

>Changes occurring in the activity of porcine pancreatic phospholipase A₂ upon formation of mixed micelles of sodium cholate and the fluorescent phosphocholines 1,2-di [6-(pyren-1-yl)butanoyl]-sn-glycero-3-phosphocholine or 1-[6-(pyren-1-yl)butanoyl]-2-[6-(pyren-1-yl)hexanoyl]-sn -glycero-3-phosphocholine were studied. A 2-fold enhancement was observed in the activity of phospholipase A₂ towards both pyrene phospholipids upon exceeding the critical micellar concentration of the system. Changes in the pyrene excimer/monomer fluorescence emission intensity ratio coincide with the enhancement of phospholipase A₂ activity at the critical micellar concentration. Due to the different effects of micellization on the alignment of the pyrene in the two fluorescent probes conformational changes could be assessed. A model describing possible conformations of these pyrene phospholipid molecules below and above the critical micellar concentration is presented and correlated with the interfacial activation of phospholipase A₂.