PURIFICATION AND CHARACTERIZATION OF A NOVEL ALPHA-CLASS GLUTATHIONE TRANSFERASE FROM HUMAN LIVER

The importance of glutathione transferases (GST) as a major group of d etoxification enzymes is well known. The human liver possesses these e nzymes in high concentration and in a multiplicity of forms. We descri be here a novel glutathione transferase isoenzyme isolated from liver using glutathione affinity chromatography, DEAE-sepharose and Mono-Q i on-exchange chromatography. The isoenzyme is a dimer of approximately 25 kDa with a blocked N-termini. Its kinetic and immunological propert ies indicate that it belongs to the alpha-l:lass of GSTs. Its isoelect ric point (8.0) is closely related to GST alpha (pl 7.8) and GST beta (pl 8.2) reported previously. More than 70% of the amino-acid sequence of this isoenzyme has been determined by automated Edman degradation procedure. The results suggest that this isoenzyme (which we term GST 8.0) may be a heterodimer of two, closely related, novel alpha-class G ST subunits. Comparisons between the amino acid sequences of these two novel alpha-class subunits with those of the other alpha-class GST su bunits already known indicate changes in a number of different residue s localized in the electrophilic binding site. Further studies are nee ded to establish whether such differences are due to allelic polymorph ism of the enzyme or to the existence of additional genes for alpha-cl ass GSTs in human liver. These results are consistent with previous da ta which suggest that a multitude of different GSTs, especially of alp ha class, are present in the human liver providing this tissue with an efficient mechanism of protection against xenobiotic and endogenous c ompounds. (C) 1998 Elsevier Science Ltd. All rights reserved.