Effect of Blue Light on Metabolism in Penicillium isariiforme

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Abstract
In blue light P. isariiforme assimilates less CO2 and excretes less citric acid into the medium than when grown in continuous darkness. This is due to a decreased supply of pyruvate which is carboxylated to form citric acid via oxaloacetate. Pyruvate carboxylase [EC 6.4.1.1] rather than phosphoenolpyruvate carboxylase or phosphoenolpyruvate carboxykinase is mainly responsible or CO2 assimilation in this fungus. Of the glycolytic intermediates assayed, steady-state concentrations of pyruvate were low and concentrations of G-6-P, glucose I-phosphate and fructose 6-phosphate were high in mycelium grown in the light compared with those in mycelium grown in the dark. Results of experiments with specifically-labeled glucose suggest that light stimulates the pentose phosphate pathway and inhibits the supply of pyruvate for citric acid synthesis via the Embden-Meyerhof-Parnas pathway.