AMINO-ACID-SEQUENCE OF PIRATOXIN-I, A MYOTOXIN FROM BOTHROPS PIRAJAI SNAKE-VENOM, AND ITS BIOLOGICAL-ACTIVITY AFTER ALKYLATION WITH P-BROMOPHENACYL BROMIDE

The complete sequence of the 121 amino acid residues of piratoxin-I (P rTX-I), a phospholipase A(2) (PLA(2))-like myotoxin from Bothrops pira jai snake (Bahia jararacussu) venom, is reported. From the sequence, a n M-r of 13,825 and an approximate pI of 8.3 were calculated. PrTX-I s hows a high sequence homology with Lys-49 myotoxins from other bothrop ic (similar to 95%) and nonbothropic (similar to 80%) venoms, but only 70-75% homology when aligned with the catalytically active Asp-49 PLA (2)s. When compared with bothropstoxin-I from Bothrops jararacussu, wh ich is morphologically almost identical to B. pirajai, only two change s out of 121 total amino acid residues have been observed. The approxi mate minimal lethal dose LD50 (mice, i.p., 24 hr) of PrTX-I was 8 (6.8 -9.1) mg/kg, and the minimal edematogenic dose (MED) in a rat paw mode l was 39.5 +/- 1.8 ug. After alkylation of His-48 with p-bromophenacyl bromide, the MED was 40.1 +/- 1.9 ug, but up to 4 LD50 were unable to cause death in any of a group of eight mice after 72 hr. Therefore th e edematogenic activity was retained and apparently did not involve Hi s-48, suggesting that at least two biologically active sites are prese nt in PrTX-I.