THE AMINO-ACID-SEQUENCE OF BOTHROPSTOXIN-II, AN ASP-49 MYOTOXIN FROM BOTHROPS-JARARACUSSU (JARARACUCU) VENOM WITH LOW PHOSPHOLIPASE A(2) ACTIVITY

The complete amino acid sequence of bothropstoxin-II (BthTX-II), a myo toxin isolated from Bothrops jararacussu snake venom, is reported. The results show that BthTX-II is an Asp-49 phospholipase A(2) (PLA(2))-l ike protein composed of a single polypeptide chain of 120 amino acid r esidues (M-r = 13,976), containing one methionine and 14 half-cystines . Despite a high degree of homology with other PLA(2)'s and the presen ce of the strategic residues known to compose the Ca2+-binding loop, n amely Tyr-28, Gly-30, Gly-32, and especially Asp-49, besides His-48, T yr-52, and Asp-99, all of them directly or indirectly involved in cata lysis, BthTX-II revealed a very low PLA(2) activity when assayed on eg g yolk phosphatidylcholine. We attribute this low catalytic activity t o the existence of extra mutations, e.g., Trp-5 for Phe-5, which point s to the need of considering other strategic positions, since only Lys -49 PLA(2)'s have been considered to be devoid of this enzymatic activ ity.