Human liver microsomal glutathione transferase: Substrate specificity and important protein sites

Abstract

Human liver microsomal glutathione transferase displays the following glutathione peroxidase/transferase activities: dilinoleoylphosphatidylcholine hydroperoxide (0.03 and 0.17 μmol min · mg, unactivated and N-ethylmaleimide-activated enzyme, respectively), linoleic acid hydroperoxide (0.09 and 0.15 μmol min · mg), cumene hydroperoxide (0.04 and 3 μmol min · mg), methyl linoleate ozonide (0.02 and 1.2 μmol min · mg) and 1-chloro-2,4-dinitrobenzene (1.9 and 24 μmol min · mg). The activation of glutathione peroxidase activities are much higher than previously observed. The activity towards a phospholipid hydroperoxide is noteworthy since protection against lipid peroxidation has been implied. Methyl linoleate ozonide has not previously been characterised as substrate for any microsomal glutathione transferase. Human liver microsomal glutathione transferase displays an isoelectric point of 9.4 and a structure in agreement with that deduced from the cDNA sequence. Gel electrophoretic analysis shows that proteolytic activation of the human enzyme corresponds to cleavage at Lys-41, thus denning the critical activation site.