SPACE-TIME DISTRIBUTION OF GAMMA-GLUTAMYL-TRANSFERASE ACTIVITY IN AGARICUS-BISPORUS

gamma-Glutamyl transferase is involved in the biosynthesis of two char acteristic gamma-glutamyl compounds occurring in Agaricus bisporus: ag aritine and gamma-glutaminyl-4-hydroxybenzene. Agaritine was shown to be a precursor of potential toxic aryl diazonium ions and gamma-glutam inyl-4-hydroxybenzene was demonstrated to be one of the main substrate s implicated in mushroom browning. gamma-G;utamyl transferase activity was measured in various tissues of A. bisporus fruitbodies at differe nt developmental stages and in mycelium grown on synthetic and compost media. Gills and skin, which exhibit the highest levels of gamma-glut amyl amino acids, also present the highest levels of gamma-glutamyl tr ansferase activity. Stipe base tissue, which is characterised by a lac k of agaritine and the presence of its hydrolysis product hydroxymethy lphenylhydrazine, also exhibits high levels of gamma-glutamyl transfer ase activity. Thus, in the gills and in the skin, gamma-Glutamyl trans ferase could be mainly involved in the synthesis of gamma-glutamyl der ivatives and, in the stipe base, in the hydrolysis of agaritine. gamma -Glutamyl transferase activity measured in mycelia was rather low but significantly greater in mycelium grown on compost medium than on synt hetic medium. These results are in agreement with the lack of gamma-gl utaminyl-4-hydroxybenzene in mycelium grown on artificial medium. Cap flesh and stipe tissues show the lowest y-glutamyl transferase activit y. The elucidation of the role of gamma-glutamyl transferase in the sy nthesis of one of the main substrates for mushroom browning opens new perspectives in attempts to optimise post-harvest quality. (C) 1998 Fe deration of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.