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Abstract: Despite the economical importance of the cultivated mushroom relatively little is known about its basic biochemistry and physiology. This study deals with the nitrogen metabolism of Agaricus bisporus and focusses on the glutamate dehydrogenases, key enzymes involved in nitrogen assimilation/dissimilation. Evidence is provided for the existence of two distinct glutamate dehydrogenases using NADH and NADPH, respectively, as a cofactor. The partial purification and the determination of some biochemical and kinetic properties are described, e.g. temperature optimum, pH optimum, stability, substrate affinity (Km values). Furthermore the possible role of the two enzymes in the metabolism of nitrogen is discussed. The activity of both enzymes was determined in the vegetative mycelium and at different stages during sporophore formation. Compared to extracts of mycelium, a strong increase of NADP - dependent glutamate dehydrogenase activity was observed in extracts of developing sporophores. The importance of this increase is discussed in relation to the factors that govern fruit body development. No differences were found in NAD -dependent glutamate dehydrogenase activity of mycelium and sporophores.
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