Isolation and characterization of a group of oligopeptides related to oxidized glutathione from the root of Panax ginseng

Abstract: Six γ‐glutamyl oligopeptides were isolated for the first time from aqueous methanol extracts of Panax ginseng root by using column chromatography on ion‐exchange resin, gel filtration and reverse‐phase high‐performance liquid chromatography. Their structures had been established with the methods of amino acid analysis, N‐terminal, C‐terminal determination and double‐coupling sequence analysis. They were: P‐I ( N ‐γ‐glutamylcystinyl‐bis‐glycine), P‐II (γ‐glutamylcysteinylglycine disulfide, oxidized glutathione), P‐III ( N,N′ ‐bis‐γ‐glutamylcystinylglycine), P‐IV (γ‐glutamylcysteinylglycinamide disulfide), P‐V ( N ‐γ‐glutamylglycylcysteine disulfide), P‐VI (γ‐glutamylarginine); five of them are related to oxidized glutathione. The structures were further confirmed by the chemical synthesis. As far as we know, P‐V ( N ‐γ‐glutamylglycylcysteine disulfide) is a new biologically active peptide which exhibits somnogenic effect and is more potent than that of P‐II.