Purification and characterization of three forms of glutathione S-transferase A. A comparative study of the major YaYa-, YbYb- and YcYc-containing glutathione S-transferases

Abstract

Rat liver glutathione S-transferases were previously defined by their elution behavior from DEAE-cellulose and CM-cellulose as M, E, D, C, B, A and AA. These enzymes are dimeric proteins which comprise subunits of MW 22,000 (Ya), 23,500 (Yb) or 25,000 (Yc). Evidence is presented that YaYa protein, one of 2 previously described lithocholate-binding proteins which exhibit transferase activity, is an additional enzyme which is not included in the M, E, D, C, B, A and AA nomenclature. It is therefore proposed that this enzyme be designated transferase YaYa. Transferases YaYa, C, A and AA have MW of 44,000, 47,000, 47,000 and 50,000, respectively and each comprises 2 subunits of identical size. These enzymes were purified to allow a study of their structural and functional relationships. In addition, transferase A was further resolved into 3 forms (A1, A2 and A3) which possess identical activities and structures and appear to be the product of a single gene. Transferases YaYa, C, A and AA each had distinct enzymic properties and were inhibited by cholate. The recently proposed proteolytic model, which attributes the presence of multiple forms of glutathione S-transferase activity to partial proteolysis of transferase AA, was tested and shown to be highly improbable. Peptide maps showed significant differences between transferases YaYa, C, A and AA. Immunotitration studies demonstrated that antisera raised against transferases YaYa and C did not precipitate transferase AA.