A lens glutathione S-transferase, class mu, with thiol-specific antioxidant activity

A protein that protected against the thiol-mediated metal-catalysed oxidati ve inactivation of enzymes but did not protect against the ascorbate-depend ent oxidation system was extensively purified from bovine lens. The protein was a homodimer (pI 7) of 26 kDa subunits. Sixty per cent of the protein s equence was obtained by Edman sequencing and by sequence comparison was det ermined to be a class mu glutathione S-transferase (GST). The sequence of t he enzyme is homologous to, but not identical to, that of any other class m u GST in the databanks. The complete protein sequence was derived from sequ encing the cDNA and is the first complete sequence of a class mu GST from a bovine tissue. The enzyme was cloned and expressed in E. coli. The recombi nant GST also protected against the thiol-mediated oxidative inactivation o f enzymes but with lower activity than the native enzyme did and the recomb inant GST had a comparable higher K-m for GSH. The native and recombinant e nzymes possessed similar low level peroxidase activity utilizing alkyl and cumene peroxides as substrates, but exhibited little activity against hydro gen peroxide.