Glutathione Breakdown and Transpeptidation Reactions in Proteus vulgaris

Abstract

THE enzymic breakdown of glutathione by animal tissues has been extensively studied¹. Both peptide bonds are split by enzymes of rat kidney homogenates; the γ-glutamyl bond is first hydrolysed to glutamic acid and cysteinylglycine, the latter being afterwards further broken down to cysteine and glycine². In 1950, Hanes, Hird and Isherwood³ demonstrated that preparations of sheep kidney not only hydrolysed glutathione, but also catalysed the transfer of the γ-glutamyl residue to the products of hydrolysis and to other added amino-acids. A more detailed analysis of the relative reactivities of various amino-acids with glutathione has recently been carried out⁴. Transpeptidation reactions were also observed between other γ-glutamyl and glycyl peptides and amino-acids in animal and plant tissues⁵. The discovery of such reactions led to speculation on their possible role in the formation of new peptides and of proteins. Although cell-free extracts of Escherichia coli synthesize glutathione from its component amino-acids⁶, these extracts do not hydrolyse the tripeptide. Breakdown of glutathione and transpeptidation in micro-organisms have not been previously reported; a study of these reactions in the bacterium Proteus vulgaris is described here.