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

Abstract

Freshly harvested, nongrowing mycelium of Neocosmospora 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 hours in water before exposure to glucose. Glucose was absorbed via two 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 two 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 water, whereas preincubated mycelium showed reduced or no leakage. The reduction in leakage due to preincubation was prevented by 5 μg/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. It is concluded that uptake of both glucose and 3-O-MG by at least the high affinity system is energy-linked and probably mediated by proton cotransport.