Oxidation of Glucoamylase from a Rhizopus sp. with N-Bromosuccinimide

概要

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Two glucoamylases from a Rhizopus sp., Gluc_1 and Gluc_2,were oxidized with N-bromosuccinimide (NBS). The number of tryptophan residues oxidized could be accurately estimated from the decrease of fluorescence intensity in 6 M guanidine hydrochloride, but not from the decrease in absorbancy at 280 nm. Gluc_1 and Gluc_2 were inactivated when about 4 to 5 tryptophan residues were oxidized. These numbers were similar to those of tryptophan residues perturbed with polyethylene glycol as a perturbant. One tryptophan residue, which existed on the surface at the N-terminal part of Gluc_1,was oxidized first, causing only a slight decrease in the enzymatic activity. Even when the enzymatic activities of Gluc_1 and Gluc_2 were destroyed by NBS oxidation, the binding abilities of Gluc_1 and Gluc_2 with maltitol were fairly well retained, because fluorescence quenching of tryptophan residues induced by the addition of maltitol was still observable. Therefore, it is suggested that these glucoamylases have at least two important tryptophan residues, one related to the catalytic action and the other related to the binding of substrates, and the latter one(s) reacts only slowly with NBS.
社団法人日本薬学会の論文
1986-03-25