Amino acid sequences of the two subunits of a phospholipase A2 inhibitor from the blood plasma of Trimeresurus flavoviridis. Sequence homologies with pulmonary surfactant apoprotein and animal lectins.

Phospholipase A2 inhibitor (PLI), purified from the blood plasma of the Habu snake (Trimeresurus flavoviridis), was separated into two distinct subunits, PLI-A and PLI-B. These subunits were shown to be glycoproteins with molecular weights of around 21,000-22,000. When they were deglycosylated chemically with trifluoromethanesulfonic acid, the molecular weights were found to be 17,000. Their amino acid sequences were determined by alignment of peptides obtained by lysyl endopeptidase digestion and Staphylococcus aureus V8 protease digestion. PLI-A and PLI-B were each composed of 147 amino acid residues with one residue, Asn103, being for N-linked glycosylation, and the molecular weights of their protein portions were calculated to be 16,368 and 16,408, respectively. Each subunit contained four cysteine residues, all of which exist in disulfide linkages (Cys64-Cys141 and Cys119-Cys133). The sequences of PLI-A and PLI-B showed 89.9% homology to each other. When the sequences were compared with those of lipocortins, no significant homologies were detected. But the sequences were significantly homologous to those of COOH-terminal carbohydrate recognition portions of pulmonary surfactant apoprotein and animal lectins.