Department of Chemistry, Faculty of Science, Tohoku University, Sendai, Japan.
The amino acid sequences of eight phospholipases A2 (Pa-1G, Pa-3, Pa-5, Pa-9C, Pa-10A, Pa-12A, Pa-12C and Pa-15) which had been isolated from the venom of Australian king brown snake (Pseudechis australis) were elucidated. Pa-1G, Pa-3 and Pa-15 showed micro-heterogeneity at the 103rd position and Pa-5 was separated into two components, Pa-5a ([Pro-18 and Tyr-61]Pa-5) and Pa-5b ([ Ser-18 and Phe-61]Pa-5). All the phospholipase A2 molecules except Pa-1Ga and Pa-1Gb which lack the 118th residue, consisted of a single chain of 118 amino acid residues including 14 half-cystine residues and all the common residues among phospholipases A2 from other sources. From comparison studies, Asp-50, Lys-58 and Asp-90 seem to be important for the toxicity, and we propose that the domain for the presynaptic toxicity consists of seven hydrophilic residues, i.e. Arg-43, Lys-46, Asp-50, Glu-54, Lys-58, Asp-90 and Glu-94.