Apparent Proteolytic Modification of Glutathione Peroxidase

Abstract

Little is known about the posttranslational processing of glutathione peroxidase (GSH-Px)(GSH:H₂O₂oxidoreductase, EC 1.11.1.9). The difference of 10 amino acids in the reported position of selenocysteine in bovine erythrocyte GSH-Px, as determined by crystallographic analysis¹ as compared to chemical sequence analysis,² suggests that a polypeptide may have been cleaved from the crystallized GSH-Px. In a study of rat liver mitochondrial GSH-Px, Voight and Autor³ reported that the initial GSH-Px gene product may be as much as 5 kDa larger than the mature enzyme. These two reports thus suggest that newly synthesized GSH-Px may be processed to a smaller molecular weight form during maturation. We have been studying various aspects of GSH-Px synthesis using immunoblotting with anti-GSH-Px antibodies to measure levels of GSH-Px protein, and using SDS-gel electrophoresis to follow ⁷⁵Se incorporation into selenoproteins. In the course of these studies, we have observed that GSH-Px can be detected in several forms that differ in their apparent molecular weight. The purpose of this report is to further describe these different molecular weight forms of GSH-Px.

Supported by the University of Arizona Experiment Station and NIH (AM 32942)