Purification and characterization of multiple glutathione transferase isoenzymes from grey mullet liver

Fourteen isoforms of glutathione S-transferase (GST) have been separated and purified from mullet (Mugil cephalus) liver by scaling up an automatic analytical method based on anionic exchange chromatography. The activity of each isoenzyme with several substrates was determined. Dimeric combinations of six subunits make up this heterogeneous isoenzyme population. Five of these were resolved by reverse phase chromatography; four of them, named a, b, c and d, were present in more than one isoform, had the same apparent molecular mass (25.2 kDa) by SDS-PAGE, and were immunochemically related to plaice GST-A and possibly to rat GST-5 but not to plaice GST-B or any other rat GST subunit; they would belong to the theta class. Subunit e was only present in isoenzyme I which was basic, had an apparent molecular mass of 23.4 kDa and would belong to the alpha class, since it was recognized by antibodies towards plaice GST-B and rat GST-1 and GST-8 and less intensely by anti-(rat)GST-2. Another subunit, named f, with 25.2 kDa apparent molecular mass that could not be distinguished by reverse phase chromatography, was detected immunochemically by positive reaction with antibodies to rat GST-1 and GST-2 in addition to reaction with anti-(plaice)GST-A. As suggested by these results we discuss the existence of genetic polymorphism, the differential expression and the evolutionary relationships of mullet GSTs.