Enzymes catalysing conjugations of glutathione with αβ-unsaturated carbonyl compounds

Abstract

1. Heat-inactivation experiments, ammonium sulphate-fractionation studies, enzyme-inhibition studies with S-(αβ-diethoxycarbonylethyl)glutathione, and evidence from the distribution of activities in rat liver, in rat kidney and in the livers of other animals, indicate that reactions of glutathione with (i) trans-benzylideneacetone, (ii) cyclohex-2-en-1-one, (iii) trans-cinnamaldehyde, (iv) diethyl maleate, (v) diethyl fumarate and (vi) 2,3-dimethyl-4-(2-methylenebutyryl)phenoxyacetic acid are catalysed by different enzymes. 2. Evidence is presented that the enzymes catalysing the reactions of glutathione with substrates (i)–(iv) are different from glutathione S-alkyltransferase, S-aryltransferase and S-epoxidetransferase. 3. The name ‘glutathione S-alkenetransferases’ is proposed for enzymes catalysing reactions of glutathione with αβ-unsaturated compounds. 4. The Arrenhius plot for the enzyme-catalysed reaction of diethyl maleate with glutathione is discontinuous, with lower energy of activation at 38°.