Inactivation Reaction of Taka-Amylase A by Ultraviolet Light

Abstract

Taka-amylase A is strongly inactivated by the irradiation of ultraviolet light, which is absorbed by amylase itself. The oxygen uptake and the amounts of oxidized amino acid residues during irradiation were measured by manometric technique and chemical analysis, respectively. The photoinactivation was attributed to the photoöxidation of amino acid residues, particularly that of cystine, tryptophan and tyrosine residues. The oxygen uptake of a solution of amylase differed little from, that of a solution of an amino acid mixture having the same molar proportions and concentrations as the amylase solution, and we may conclude that the formation of a high polymer structure or of a special conformation of amylase molecule does not measurably affect the oxygen uptake. The photoinactivation is enhanced by the presence of paramagnetic ions, but not by the presence of diamagnetic ions. This was attributed to the spin-orbit coupling by the inhomogeneous magentic field of the paramagnetic ions. An addition of a substrate inhibits considerably the photoinactivation. The effect may be due to the capture of the photoelectron ejected from amino acid residues and/or HO2 by the substrate and decomposition products. © 1966, Japan Society for Bioscience, Biotechnology, and Agrochemistry. All rights reserved.