STRUCTURE AND PROPERTIES OF A HOMOLOGUE OF GLUTATHIONE

Abstract

Evidence for the structure of a new disulphide peptide isolated from etiolated seedlings of Phaseolus aureus is presented. The peptide is bis-L-gamma-glutamyl-L-cystinyl-bis-[beta]-alanine, which, in the thiol form, is a higher homologue of glutathione, and has thus been called homoglutathione (homo GSSG). Oxidized glutathione is much more soluble than homoGSSG. The pK3 and pK4 values of homoGSSG are appreciably higher than the corresponding values of GSSG. Some chromatographic and electrophoretic properties of homoGSSG, homoGSH, the sulphonic acid derivative of homoGSSG and the N-ethylmaleimide adduct of homoGSH are listed. Carboxy-peptidase A does not hydrolyse the cystinyl-[beta]-alanine bond of homoGSSG. HomoGSH is an activator of glyoxalase but has only 55% of the activity of GSH. HomoGSSG will oxidize NADPH in the presence of glutathione reductase.