Isolation and characterization of a phospholipase A2 inhibitor from the blood plasma of the Thailand cobra Naja naja kaouthia.

A phospholipase A2 (PLA2) inhibitory protein was purified from the blood plasma of the Thailand cobra Naja naja kaouthia by sequential chromatography on Sephadex G-200, DEAE Affi-Gel Blue, and Protein-Pak G-Butyl columns. The purified inhibitor was a glycoprotein with an apparent molecular mass of about 90 kDa and contained 25- and 31-kDa subunits with a molar ratio of 1:2. The 31-kDa subunit contained a glycosidic chain and the molecular mass was reduced to 28 kDa by N-glycosidase F treatment. The amino acid compositions of the two subunits were characterized by their high content of cysteine residues. The inhibitor inhibited group II as well as group I PLA2's. Since the fundamental properties were different from those of the two Crotalidae inhibitors already reported, the cobra inhibitor might be a new type of PLA2 inhibitor.