A New Sulfur-containing Peptide from Lentinus edodes Acting as a Precursor for Lenthionine

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A sulfur-containing peptide, acting as an enzymatic precursor of the aroma-bearing substance, was isolated in crystalline form from fruiting bodies of the shiitake mushroom. The isolation procedure consists of methanol extraction, repeated ion-exchange chromatographies, and crystallization from methanol-water. The common name “lentinic acid” is given for the isolated peptide. Amino acid analysis, performed after acid hydrolysis of the oxidized or desulfurized peptide, indicates involvement of a glutamic acid and S-sub-stituted cysteine sulfoxide in the molecule. Results of enzymatic assays led to the designa-tion of L-configuration for the component amino acids. The presence of a r-glutamyl peptide bond is shown, since glutamic acid constitutes the N-terminal amino acid and a free amino group is adjacent to a free carboxyl group. The structure proposed for lentinic acid is,
CH₃SO₂-[C₃H₆O₂S₂]-S(O)CH₂CH(COOH)NHCOCH₂CH₂CH(NH₂)COOH.
The precise structure for the portion in brackets is unidentified.