Some factors regulating [1-¹⁴C] acetate incorporation into aflatoxins by spheroplasts and spheroplast lysates from Aspergillus parasiticus

Abstract

Factors regulating aflatoxin biosynthesis were studied in spheroplasts and lysates of Aspergillus parasiticusNRRL 3240. Over a 2 hr period, ribose, sucrose and maltose stimulated the incorporation of [1-¹⁴C] acetate into aflatoxins. Of a number of inorganic salts studied, zinc sulphate, magnesium sulphate, cobaltous chloride, cadmium acetate and strontium chloride stimulated the incorporation of labeled acetate into aflatoxins. Vanadyl sulphate and ferrous sulphate inhibited de novo aflatoxin formation in spheroplast lysates. Strontium chloride at concentrations of 0·01-0·5 mM stimulated [1-¹⁴C] acetate incorporation. Silver nitrate, copper sulphate and chlorides of manganese, calcium and barium markedly stimulated the incorporation of radioactivity into aflatoxins. An inverse correlation between the incorporation of [1-¹⁴C] acetate into aflatoxins and lipids was noted. In lysates, addition of pyruvic acid markedly increased de novo aflatoxin synthesis. Acetoacetate and bicarbonate enhanced incorporation of radioactivity at lower concentrations. Citric acid at 1-10 mM concentrations was stimulatory to incorporation of label into aflatoxins while malonic acid was inhibitory. In lysates, EDTA enhanced acetate incorporation into aflatoxins and inhibited incorporation of label in intact spheroplasts. This effect was only partially reversed by the addition of ZnSO₄ or MgSO₄.