Effect of Radical Anions on the Inactivation of Glucose Isomerase

Abstract

The inactivation of glucose isomerase by radiolytically generated radical anions was investigated. In a pure solution of the enzyme at pH 7.0, Br^- had a pronounced radiosensitizing action whereas CNS^- had a protective action. The Br^- did not sensitize the inactivation of the enzyme irradiated at higher pH levels. From these results, it was estimated that the histidine residue is essential for the activity of glucose isomerase. The inactivation of the enzyme with diethylpyrocarbonate, which is a selective modification reagent of histidine residues, supports this estimation.
The inactivation of glucose isomerase in the Streptomyces cell was also accelerated markedly by Br^-. KCNS, tert-BuOH and O₂, which all had a protective action in vitro, accelerated the inactivation in vivo, although the sensitizations were smaller than that of Br^-. Since these materials could not directly attack the active site of glucose isomerase, the inactivation would be accelerated by indirect action such as a destruction of the protective substances in the cell.