Utilization of Carbohydrates by Rhynchosporium secalis II. Absorption and Metabolism of Glucose, Galactose and Galacturonic acid.

Glucose, galactose and galacturonic acid were taken up at different rates by the fungus Rhynchosporium secalis and were intracellularly converted to other forms of carbohydrate at different rates. These differences explain why, when there is only a single source of nutrient carbon in the growth medium, development of the fungus is greatest when glucose is present and least when galactose is present. Glucose and galactose were taken up by the same mechanism for their uptake showed a reciprocal competitive inhibition. Uptake mechanisms had a high affinity for glucose (apparent Km 2.76 mM) and galacturonic acid (apparent Km 3.10 mM) and a low affinity for galactose (apparent Km 29.67 mM). After uptake, galactose accumulated in the mycelium, whereas glucose and galacturonic acid were rapidly converted to other soluble carbohydrates, principally trehalose and mannitol. The insoluble carbohydrates within the mycelium were little affected by the type of carbohydrate that was supplied to the fungus. [ABSTRACT FROM AUTHOR]