Chemical modification of bacillus-thuringiensis subsp aizawai delta-endotoxin - implication of arginine residues in bombyx-mori toxicity

A purified protein fraction of Bacillus thuringiensis subsp. aizawai (HD-133)-activated toxin was subjected to amino acid modification by phenylglyoxal as an arginine-directed reagent. The effect of phenylglyoxylation was assayed on the K (+)-dependent accumulation of leucine into brush border membrane vesicles from Bombyx mori larval midgut. Phenylglyoxal inactivates the toxin in a dose-and time-dependent manner. Loss of inhibitory effect of the toxin followed a pseudo-first-order kinetics. Observed rates of inactivation were linearly dependent upon the square of phenylglyoxal concentration and a second-order constant of 4.17 M(-2) min(-1) was calculated. These results indicate the involvement of highly reactive arginine residues in the formation of specific toxin domains implicated in the interaction with membrane receptor(s)