Tryptophan residues of saccharifying alpha-amylase from Bacillus subtilis. A kinetic discrimination of states of tryptophan residues using N-bromosuccinimide.

Four tryptophan residues of saccharifying alpha-amylase from B. subtilis out of eleven in total are reactive towards N-bromosuccinimide (NBS), suggesting that they are on the surface of the enzyme. This is consistent with the results of solvent perturbation difference spectrophotometry with ethylene glycol. One of four tryptophan residues was clearly distinguished from the other three in reactivity with NBS by the stopped-flow method. This most reactive tryptophan residue was not protected from modification by substrates of analogs, indicating that the tryptophan is not located in the substrate binding site. One of the other three tryptophan residues, probably the second most reactive one, is considered to be related in some way to the glycosyl transfer in the reaction of the enzyme with maltose as a substrate.