Studies on water-soluble nonprotein amino acids and oligopeptides from Panax species

Previous studies of nonprotein amino acids and oligopeptides in Panax speci es including Panax ginseng, Panax notoginseng etc., were reviewed. gamma - Amino butyric acid (GABA), neuroexcitotoxic nonprotein amino acid, beta - N - oxalo - L - alpha, beta - diaminopropiomc acid (P - N - L - ODAP), P - a lanine and other substances were isolated and identified from Panax species . Seven gamma - glutamyl oligopeptides were isolated for the first time fro m aqueous extracts of Panax ginseng root. They were identified as: P - I (o xidized glutathione, GSSG), P - II (oxidized glutathione amide), P - III ( N - gamma - glutamylglycylcysteine disulfide, IGSSG), P - N ( N - gamma - g lutamylcystinyl - bis - glycine), P - V ( N, N' - bis - gamma - glutamylcys tinylglycine), P - IV (gamma - glutamylarginine) and P - VII (reduced gluta thione GSH). Six of them are related to oxidized glutathione. The structure s of P - II to P - VI were further confirmed by syntheses. P - III is appar ently a new biologically active peptide which exhibits somnogenic effects. It is more potent than P - I. The neurophysiological activity of P - N - L - ODAP and GABA as well as other bioactivities are also discussed.