Phospholipase A2 catalyzes the stereospecific cleavage of the sn-2 acyl ester union of diacyl-glycerophospholipids and liberates 1-acyl-2 lysophospholipids and free fatty acids. The novel secretory Phospholipase A2 enzyme from soybean (Glycine max)(1), denoted as GmsPLA2-I, has been characterized with respect to substrate preference and optimum conditions of catalysis. The effect of the head-group charge of the phospholipids substrate on the GmsPLA2 catalyzed hydrolysis was examined through initial rate kinetic measurements of the free fatty acid liberated by the enzyme activity towards mixed micelles of phospholipid/Triton X-100 in a Colorimetric assay. The substrates used in this studies were 1,2-dilauroyl-sn-glycero-3-phosphate (DLPA),1,2dilauroyl-sn-glycero-3-phosphoethanolamine (DLPE) ,1,2-dilauroyl-sn-glycero-3-phospho-(1'-rac-glycerol) (DLPG) and dilauroylphosphatidylcholine (DLPC). The optima of pH, temperature, and calcium concentration were found to be similar to the parameters of secretory PLA2s from other plants and animals. However, substrate preferences markedly differed. In contrast to pancreatic sPLA2(2), GmsPLA2-I preferred zwitterionic phospholipids, and showed lower activity toward anionic phospholipids. This way, the sPLA2-I enzyme shows more activity towards PC > PE > PG > PA. Moreover, the kinetic parameters (Vmax and KM) for DLPG and DLPC substrates were determined.
