Uptake and Metabolism of d-Glucose by Neocosmospora vasinfecta E. F. Smith

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Abstract
Freshly harvested, nongrowing mycelium of N. vasinfecta E.F. Smith rapidly absorbed exogenous glucose but converted a greater proportion to trehalose and glucan than to respiratory CO2. This effect was accentuated in mycelium preincubated for 3.5 h in H2O before exposure to glucose. Glucose was absorbed via 2 uptake systems, both apparently constitutive, with apparent Km values for glucose of 0.02 mM (high affinity) and 2 mM (low affinity). The glucose derivative 3-O-methylglucose (3-O-MG) was also absorbed by 2 apparently constitutive systems with apparent Km values for 3-O-MG of 0.065 mM and 1.9 mM. Absorption of 3-O-MG by both freshly harvested and preincubated mycelium led to its accumulation. Freshly harvested mycelium lost accumulated 3-O-MG rapidly to H2O, whereas preincubated mycelium showed reduced or no leakage. The reduction in leakage due to preincubation was prevented by 5 .mu.g/ml cycloheximide in the preincubation medium. Glucose competitively inhibited 3-O-MG uptake via the high affinity system and induced loss of previously accumulated 3-O-MG from preincubated mycelium. The uptake of both glucose and 3-O-MG was associated with a transient alkalinization of the uptake medium. Uptake of both glucose and 3-O-MG by at least the high affinity system apparently is energy-linked and probably mediated by proton cotransport.