title: The metabolic pathway catalyzed by the tyrosinase of Agaricus bisporus.
abstract: N-t-Butyloxycarbonyl-gamma-L-glutaminyl-2-bromo-4-hydroxybenzene alpha-benzyl ester was synthesized as a precursor to gamma-L-glutaminyl-4-hydroxy[2-3H]benzene. With this labeled compound and the previously synthesized gamma-L-glutaminyl-4-hydroxy[3,5-3H]benzene, the stoichiometry of ring substitution was determined for the tyrosinase-catalyzed metabolic pathway of Agaricus bisporus. In this pathway, gamma-L-glutaminyl-4-hydroxybenzene is hydroxylated to gamma-L-glutaminyl-3,4-dihydroxybenzene which is oxidized to gamma-L-glutaminyl-3,4-benzoquinone and a compound of previously unknown structure, "490." The results indicated that the "490" quinone was derived from gamma-L-glutaminyl-3,4-benzoquinone without further ring substitution. A base-catalyzed, nonenzymatic reaction of gamma-L-glutaminyl-3,4-benzoquinone was observed which yielded a compound with a 490 nm chromophore. gamma-Glutamyl transpeptidase cleavage of gamma-L-glutaminyl-3,4-dihydroxybenzene led to the release of 4-aminocatechol which air-oxidized to a compound with identical spectral properties to "490." The structure of "490" was thus determined to be 2-hydroxy-4-imino-2,5-cyclohexadiene-1-one(2-hydroxy-4-iminoquinone). The tyrosinase-catalyzed hydroxylation of gamma-L-glutaminyl-4-hydroxybenzene was found to be optimal at pH 8.0, while the enzymatic oxidation of gamma-L-glutaminyl-3,4-dihydroxybenzene was optimal at pH 6.0.
mesh_terms: D000363:Agaricales / Q000201:enzymology*; D004156:Catechol Oxidase / Q000378:metabolism*; D005973:Glutamine / Q000031:analogs & derivatives / Q000138:chemical synthesis / Q000378:metabolism; D006899:Mixed Function Oxygenases / Q000378:metabolism; D014442:Monophenol Monooxygenase / Q000378:metabolism*; D010088:Oxidoreductases / Q000378:metabolism; D010636:Phenols / Q000138:chemical synthesis / Q000378:metabolism; D013053:Spectrophotometry; D005723:gamma-Glutamyltransferase / Q000378:metabolism
chemical_list: D010636:Phenols; D005973:Glutamine; C001298:gamma-L-glutaminyl-4-hydroxybenzene; D006899:Mixed Function Oxygenases; D010088:Oxidoreductases; D004156:Catechol Oxidase; D014442:Monophenol Monooxygenase; D005723:gamma-Glutamyltransferase