Glutathione S-transferases. the First Enzymatic Step in Mercapturic Acid Formation.

The purification of homogeneous glutathione S-transferases B and C from rat liver is described. Kinetic and physical properties of these enzymes are compared with those of homogeneous transferases A and E. The letter designations for the transferases are based on the reverse order of elution from carboxymethylcellulose, the purification step in which the transferases are separated from each other. Transferase B was purified on the basis of its ability to conjugate iodomethane with glutathione, whereas transferase C was purified on the basis of conjugation with 1,2-dichloro-4-nitrobenzene. Although each of the four enzymes can be identified by its reactivity with specific substrates, all of the enzymes are active to differing degrees in the conjugation of glutathione with p-nitrobenzyl chloride. Assay conditions for a variety of substrates are included. All four glutathione transferases have a molecular weight of 45,000 and are dissociable into subunits of approximately 25,000 daltons. Despite the similar physical properties and overlapping substrate specificities of these enzymes, only transferases A and C are immunologically related.