EFFECTS OF TEMPERATURE AND GLYCERIDES ON THE ENHANCEMENT OF AGKISTRODON PISCIVORUS PISCIVORUS PHOSPHOLIPASE A(2) ACTIVITY BY LYSOLECITHIN AND PALMITIC ACID

The effect of temperature and various glycerides to modulate the abili ty of lysolecithin and fatty acid to promote high phospholipase A(2) a ctivity was studied using dipalmitoylphosphatidylcholine large unilame llar vesicles as substrate. The length of the lag phase prior to the a ccumulation of sufficient hydrolysis products (lysolecithin and fatty acid) to support high phospholipase activity was shortest at temperatu res near the thermotropic phase transition of the phospholipid substra te. A reduction in the lag phase correlated with a reduction in the re quirement for hydrolysis products at the phase transition temperature, where the bilayer exists in a state of fluctuating domains of gel and liquid crystal. Dipalmitoylglycerol and tripalmitoylglycerol also red uced the length of the lag phase. This reduction was both concentratio n-dependent and temperature-dependent relative to the phase transition in the presence of the glycerides. As with the effect of temperature, the ability of di- and triglycerides to decrease the lag time correla ted with a decrease in the amount of reaction products necessary to pr omote high phospholipase activity. This effect coincided with the tend ency of the glycerides to form domains in the bilayer. Glycerides that did not form domains either had no effect (monopalmitoylglycerol) or increased the length of the lag phase (dicaprylglycerol). These data s uggest that the effect of the reaction products to increase phospholip ase A(2) activity is aided by the presence of fluctuations in lipid do mains within the bilayer.