The single cysteine residue on an alpha family chick liver glutathione S-transferase CL 3-3 is not functionally important

Chick liver glutathione S-transferase CL 3-3, expressed using a baculovirus system in Spodoptera frugiperda (SF9) cells, contains a single cysteine residue per subunit. This enzyme was modified with iodoacetamide. Amino acid analysis indicates that 0.85 +/- 0.10 cysteine residue was modified per enzyme subunit. GST CL 3-3 modified with iodo[14C]acetamide was further digested with trypsin and the isotope-labelled fragments were isolated. The fragment containing the cysteine residue accounts for 53% of the total labels. The S-carbaminomethylated protein retains the glutathione conjugating activity. Therefore, the cysteine residue is not essential for the enzymatic activity of CL 3-3.