Isolation and amino acid sequence of a phospholipase A2 inhibitor from the blood plasma of Agkistrodon blomhoffii siniticus.

Phospholipase A2 inhibitor (PLI) was purified from the blood plasma of Chinese Mamushi, Agkistrodon blomhoffii siniticus, by sequential chromatography on Sephadex G-200, Mono Q, and Blue-Sepharose CL-6B columns. The purified PLI was a glycoprotein with an apparent molecular mass of 75 kDa and was composed of a single subunit with a mass of about 20 kDa. From the results of a cross-linking experiment, the PLI was found to present as a homotrimer of the subunit. The fundamental properties of A. blomhoffii siniticus PLI were very similar to those of Habu Trimeresurus flavoviridis PLI [Kogaki et al. (1989) J. Biochem. 106, 966-971], although the latter was composed of two homologous subunits, PLI-A and PLI-B [Inoue et al. (1991) J. Biol. Chem. 266, 1001-1007]. The amino acid sequence of the subunit of A. blomhoffii siniticus PLI was determined by alignment of the peptides obtained by lysyl endopeptidase digestion or Staphylococcus aureus V8 protease digestion. The subunit was composed of 147 amino acid residues with one residue, Asn103 being N-glycosylated. The molecular weight of its protein portion was calculated to be 16,444 Da. The amino acid sequence of A. blomhoffii siniticus PLI subunit showed about 75% homology to those of T. flavoviridis PLI subunits, and also showed significant homologies to those of the carbohydrate recognition domains of C-type lectins.