Amino Acid Profiles of Common Cultivated Mushrooms Including the Identification of N-(N-γ-L-Glutamyl-3-Sulfo-L-Alanyl)Glycine in Flammulina velutipes

Amino acid profiles of nonprotein nitrogen (NPN) and protein nitrogen (PN) fractions of common cultivated mushrooms were determined. Free amino acids in the NPN fractions were generally characterized by the predominant occurrence of alanine and amino acids metabolically related to the glutamic acid family and also by the common presence of unique nonprotein amino acids, such as saccharopine, cystathionine and ethanolamine. A novel glutathione analog, N-(N-γ-L-glutamyl-3-sulfo-L-alanyl)glycine, was found in Flammulina velutipes. The proportion of the NPN to the total nitrogen was relatively high and large amounts of the NPN were made up of free amino acids and related compounds. Protein amino acids in the NPN and PN fractions accounted for about 65% of the total nitrogen, suggesting that a practical nitrogen-protein conversion factor for the mushrooms may be considered to be about 4 on the average.