Different forms of human liver glutathione s-transferases arise from dimeric combinations of at least four immunologically and functionally distinct subunits

Abstract

Four immunologically distinct subunits were characterized in glutathione (GSH) S-transferases of human liver. Five cationic enzymes (pI 8.9, 8.5, 8.3, 8.2 and 8.0) have an apparently similar subunit composition, and are dimers of 26 500-Mr (A) and 24 500-Mr (B) subunits. A neutral enzyme, pI 6.8, is a dimer of B-type subunits. One of the anionic enzymes, pI 5.5, is also a dimer of 26 500-Mr subunits. However, the 26 500-Mr subunits of this anionic enzyme form are immunologically distinct from the A subunits of the cationic enzymes, and have been designated as A'. Immunoabsorption studies with the neutral enzyme, BB, and the antibodies raised against the cationic enzymes (AB) indicate that A and B subunits are immunologically distinct. Hybridization in vitro of the A and B subunits of the cationic enzymes (AB) results in the expected binary combinations of AA, AB and BB. Studies with the hybridized enzyme forms indicate that only the A subunits express GSH peroxidase activity. A' subunits have maximum affinity for p-nitrobenzyl chloride and p-nitrophenyl acetate, and the B subunits have highest activity towards 1-chloro-2,4-dinitrobenzene. The other anionic form, pI 4.5, present in liver is a heterodimer of 22 500-Mr (C) and B subunits. The C subunits of this enzyme are probably the same as the 22 500-Mr subunits present in human lung and placental GSH transferases. The distinct immunological nature of B and C subunits was also demonstrated by immunoaffinity and subunit-hybridization studies. The results of two-dimensional polyacrylamide-gel-electrophoretic analyses indicate that in human liver GSH transferases, three charge isomers of Mr 26 500 (A type), two charge isomers of Mr 24 500 (B type) and two charge isomers of Mr 22 500 (C type) subunits are present.

Interaction of hemin with placental glutathione transferase

“…It is possible that the differences in the results could be due to the different experimental conditions. However, it has to be noted that the acidic GSH transferase of liver and placenta appears to be structurally different [29]. The lower affinity site for hemin found in the placental enzyme has a dissociation constant which is very similar to the value reported by Takikawa for the acidic human liver GSH transferase [18].…”

Subunit Heterogeneity of Cationic Human Hepatic Glutathione S-Transferases

“…Neither Soma et al [ 14] nor Stockman et al [ 13] employed urea SDS-PAGE which we found to be a convenient method for identi fication of the subunit composition of the purified proteins. Our results along with these other two laboratories seem to be dif ferent from Singh et al [23] with respect to subunit composition of the human hepatic transferases.…”

“…They found two subunits for forms 8 and e on urea SDS-PAGE. Further work by this group has suggested that five forms of cationic transferase resolved on iso electric focusing are all heterodimers [23], This suggestion has not been confirmed by others [this report, ref. 13,14].…”

“…However, sub unit heterogeneity of the human cationic GSH S-transferases was first suggested by Dao et al [23]. They found two subunits for forms 8 and e on urea SDS-PAGE.…”

Special article the glutathione S-transferases: An update

“…13 different forms of GST have been identified in human liver (13). These human isozymes are formed by different combinations of a t least four different subunits (13,29). The nomenclature applied to the rat has not, been used for man or other species, making comparison ofthe different enzymes difficult.…”