COMPLETE PRIMARY STRUCTURE OF THE SUBUNITS OF HETERODIMERIC PHOSPHOLIPASE A(2) FROM VIPERA A ZINNIKERI VENOM

Molecular weight determination of dimeric phospholipase A(2) from Vipe ra aspis zinnikeri venom (PLA(2)-I) was performed with electrospray io nization mass spectrometry (ESI-MS). PLA(2)-I consists of an acidic an d a basic subunit (subunit A and B), which bind noncovalently and diss ociate under highly acidic conditions. The protonated molecular ions o f subunit A and B were measured to be 13,655.9 and 13,842.6, respectiv ely. The complete amino acid sequence was also determined by Edman seq uencing of the S-pyridylethylated derivative and its peptides derived from enzymatic digestion, Both subunit A and B consist of 122 amino ac id residues and contain 7 disulfide bonds. The theoretical molecular m ass calculated from the primary structure completely agree with the ES I-RIS data. The sequential homology between subunit A and B was 63.9%; however, subunit A lacks enzymatic and biological activities that are characteristic for phospholipase A(2). Although the amino acid residu es essential for calcium binding (Tyr(28), Gly(30), Gly(32), and Asp(4 9)) and catalysis (Asp(92)) were preserved, replacement of functionall y important residue (His(48)) for catalysis with a Gin was found in su bunit A. In addition, substitution of acidic amino acid residues for b asic ones and hydrophilic residues for hydrophobic ones were observed in subunit A. Presumably, these changes in the primary structure of su bunit A resulted in the loss of enzymatic activity and an increase in the binding ability with subunit B. (C) 1996 Academic Press, Inc.