Affinity purification and characterization of glutathione S-transferases from bovine liver

Conditions have been investigated for the use of triazine dye agarose as an affinity matrix for the purification of glutathione S-transferases from bovine liver. Orange A agarose was most suitable for this purpose among various dye agaroses tested. The enzymes were adsorbed on the dye agarose column and then completely eluted with the buffer containing 1 mM reduced glutathione. Thus, a simple and rapid method for purification of bovine liver transferases was developed, which uses column chromatographies on orange A agarose followed by DEAE-Sephacel. One step of the affinity chromatography provided 40-fold purification. Upon chromatography on DEAE-Sephacel, the enzyme activity separated into two major forms (I and II), which were purified to apparent homogeneity as examined by polyacrylamide gel electrophoreses. The pI values of the two forms, I and II, were 6.7 and 6.1, respectively. The overall extents of purification of I and II were about 40-fold and 50-fold, respectively. The activities of the two major enzymes toward various substrates were roughly similar. The optimum pH values of these enzymes were 7.5 as measured with o-dinitrobenzene as a substrate. The activities were significantly inhibited by Cu2+, Hg2+, Cd2+, and Zn2+. In sodium dodecyl sulfate-polyacrylamide gel electrophoresis, both enzymes showed one band with a molecular weight of about 27,000. Both enzymes, however, were eluted as a single peak from a Sephadex G-150 column at a position corresponding to a molecular weight of about 49,000. These results show that each enzyme consists of two subunits bound to each other non-covalently. The amino acid compositions showed characteristically high contents of leucine and aspartic acid residues. Double immunodiffusion showed complete identity of the two forms reacting with both rabbit anti-enzyme sera. The two enzymes had an identical amino-terminal amino acid sequence as follows: H-Pro-Met-Ile-Leu-Gly-Tyr-Trp-Asp-Ile-Arg-Gly-Leu-Ala-His-Ala-Ile-Ser-Le u-Leu-Leu.