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Abstract: Mannitol is accumulated in the fmit bodies of Agaricus bisporus (up to 30% of the d w ), whereas its concentration in mycelium is significantly lower (1-5% of the d w ) Mannitol probably acts as an osmoticum during active growth of the sporophores and is synthesized through the reduction of fmctose by mannitol dehydrogenase (MD) In contrast, glycogen and trehalose accumulate in the mycelium Some evidence exists that glycogen and trehalose supply a significant proportion of the carbon for growth of fruit bodies (e g mannitol synthesis) and that their peak levels in mycelium are related to the productivity of the emerging flush A bisporus does neither possess an acid or neutral trehalase nor the trehalose synthesizing complex Instead a trehalose Phosphorylase (TP) was identified and purified Under physiological conditions, TP probably performs both synthesis and degradation of trehalose Further data are presented on enzyme activities and carbohydrate levels in axenic cultures of two wild-type strains of A bisporus, with special emphasis to the physiological role of TP The enzymes TP, MD and glucose-6-phosphate dehydrogenase (G6PD) seem to be developmentally regulated, in contrast to hexokinase (HK) Hyphal aggregates showed higher activities of TP (measured in the direction of trehalose degradation), MD and G6PD compared to the mycelium, whereas HK activity varied little In the period preceding the axenic formation of hyphal aggregates, synthesis of trehalose by TP approximately doubled in the mycelium The carbohydrate levels varied in a way similar to their corresponding enzymes
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