The activity of glucose-6-phosphate dehydrogenase changes when the mycelium is grown on different carbon sources. In the presence of ribose, the activity of the enzyme is approximately 3 times higher than when the mycelium is grow in a medium containing glucose. This increase in the enzyme activity is developed progressively when the concentration of ribose increases from 1% to 6% and it is blocked if cycloheximide is added to the medium. This results suggest an increase in "de novo" synthesis of the enzyme rather than an specific activation of the latent enzyme. Three isoenzymes of glucose-6-phosphate dehydrogenase are isolated from mycelium grown on ribose, whereas only two isoenzymes are isolated from mycelium grown on glucose.

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