Resting cell studies on formation of water-soluble red pigments byMonascus sp.

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Abstract
A resting cell system was developed for the biosynthesis of soluble red pigments byMonascus. The medium contains glucose, glycine, ZnSO4 and MnSO4 in pH 7.0 MOPS buffer containing cycloheximide to prevent protein synthesis. The linear production observed over a period of at least four h was due to de novo polyketide synthesis and biological methylation, as shown by inhibition with cerulenin, iodoacetamide and ethionine. Production was inhibited by carbonyl reagents and stimulated by pyridoxamine suggesting that the conversion of endogenous intracellular orange pigments to extracellular red pigments involves Schiff base intermediates and vitamin B6 a cofactor. The resting cell system was used to study the mode of action of nutritional effectors previously pinpointed by experiments with growing cells. The negative effects of high concentrations of phosphate and Mg++ are due to inhibition of pigment synthase action, not to repression or inactivation of these enzymes. The positive effects of trace metals, especially Zn++, are due to stimulation of growth and enzyme action, not to induction or stabilization of the synthases.