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

A protein that protected against the thiol-mediated metal-catalysed oxidative inactivation of enzymes but did not protect against the ascorbate-dependent 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 sequence was obtained by Edman sequencing and by sequence comparison was determined to be a class mu glutathione S-transferase (GST). The sequence of the enzyme is homologous to, but not identical to, that of any other class mu GST in the databanks. The complete protein sequence was derived from sequencing 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 recombinant GST also protected against the thiol-mediated oxidative inactivation of enzymes but with lower activity than the native enzyme did and the recombinant GST had a comparable higher K(m)for GSH. The native and recombinant enzymes possessed similar low level peroxidase activity utilizing alkyl and cumene peroxides as substrates, but exhibited little activity against hydrogen peroxide.