ISOLATION OF A HOMOLOGUE OF GLUTATHIONE AND OTHER ACIDIC PEPTIDES FROM SEEDLINGS OF PHASEOLUS AUREUS

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Abstract
The expressed juice from etiolated seedlings of P. aureus was fractionated on an anion-exchange resin and the acidic compounds were then fractionated by gel-filtration chromatography on Sephadex G 25. The main dipeptide was gamma-glutamylmethionine. In other experiments gamma-glutamyl-S-methyl-cysteine was the major dipeptide. Homoglutathione was separated from other acidic peptide-like compounds on a column of DEAE -Sephadex A50. Other peptide-like compounds contained a complex mixture of amino acids among which glutamic acid, cystine, [beta]-alanine, aspartic acid and glycine predominated. Small amounts of glutathione were also present. In the fresh juice homoglutathione was in the thiol form, in a concentration of approximately 0.1-0.3 [mu]mole/ml of juice. The ratio of homoglutathione to glutathione was probably greater than 181. Chromatographic and electrophoretic methods for distinguishing between homoglutathione and glutathione are described. The occurrence of thiol peptides and recently discovered peptides in plants is reviewed. The occurrence of [beta]-alanine in peptides is discussed. Urea was found in 1 of the fractions but was not present in the freshly expressed juice. It is thought that urea was produced from allantoic acid during the fractionation.