Binary combinations of four protein subunits with different catalytic specificities explain the relationship between six basic glutathione S-transferases in rat liver cytosol.

Abstract

Six forms of glutathione S-transferases with basic isoelectric points have been isolated from rat liver cytosol.The purification procedure consists of affinity chromatography on S-hexylglutathione bound to epoxy-activated Sepharose 6B followed by chromatofocusing.The six proteins can be classified into two groups, one reacting with antibodies to glutathione S- transferase B and one reacting with antibodies to glutathione S-transferase C. The three proteins in the first group are composed of two subunits, Y, (Mr = 22,000) and Y, (M, = 25,000), in the three possible combinations.The three proteins in the second group are corresponding combinations of two subunits of similar size, Yb and Yrb (Mr = 23,500).The relative specific activities obtained with different substrates clearly distinguish the various forms from each other.Transferases of "Btype'' have high glutathione peroxidase activity, but negligible activity with bromosulfophthalein or truns-4-phenyl-3-buten-2-one.The Y, subunit has high activity with AS-androsten-3,17-dione andp-nitrophenyl acetate and low activity with ethacrynic acid.It can be distinguished from the Y, subunit, which has high activity with ethacrynic acid and low activity with the other two substrates.The heterodimer, Yay,, has specific activities between those of the dimers, Yay, and Y,Y,.The second group of transferases have low glutathione peroxidase activity and high activity with either bromosulfophthalein or trans-4-phenyl-3-buten-2, me.The Yb and Y'b subunits are distinguished by giving high activity with bromosulfophthalein and tnzns-4-phenyl-3-buten-2-one, respectively.Glutathione S-transferases A, AA, B, and C correspond to protein dimers YbYb, Y,Y,, Yay,, and YbY'b, respectively.A new nomenclature for these transferases is proposed, in which the subunits Y,, Yb, Y'b, and Y, are designated by L, A, C, and B, and the enzymes are denoted as glutathione S-transferases Lz, BL, etc., according to their subunit composition.The glutathione transferases (EC 2.5.1.18)are known as a