SEQUENCE DETERMINATION AND CHARACTERIZATION OF A PHOSPHOLIPASE-A2 ISOZYME FROM TRIMERESURUS-GRAMINEUS (GREEN HABU SNAKE) VENOM

In addition to phospholipase A2-I (PLA2-I) reported previously (ODA et al., 1991, Toxicon 29, 157), a new PLA2 named PLA2-II was isolated from Trimeresurus gramineus (green habu snake) venom, and its amino acid sequence was determined by sequencing the native protein and the peptides produced by enzymatic (Achromobacter protease I and clostripain) cleavages of the carboxamidomethylated derivative of the protein. The protein consisted of 122 amino acid residues and His-47, Asp-48, and Asp-98 which have been assumed to be essential for PLA, activity were conserved. Its sequence similarity to PLA2-I was 79%, with 26 residual differences. In contrast to the unique presence of Phe-28 in PLA2-I, PLA2-II contains Tyr-28 as seen in most of other PLA2s. There was no significant difference between the dissociation constants of PLA2-I and PLA2-II for Ca2+ Secondary structure compositions of PLA2-II were similar to those of PLA2-I and Crotalus atrox PLA2. A striking difference was found between these isozymes in contractile activity of isolated smooth muscle preparation of guinea-pig ileum. PLA2-II was over ten times more potent than PLA2-II although its lipolytic activity toward egg-yolk was even slightly weaker (73%) than that of PLA2-I. The difference in contractile activities of PLA2-I and PLA2-II could be assumed to be due to discriminative lipid recognition brought about by different amino acid residues at the 58th position (Asp for PLA2-I and Asn for PLA2-II).