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CONTROL OF ISOCITRATASE FORMATION IN RHIZOPUS NIGRICANS

Department of Biological Sciences and Graduate Division of Microbiology, University of Cincinnati, Cincinnati, Ohio

ABSTRACT

WEGENER, WARNER S. (University of Cincinnati, Cincinnati, Ohio), AND ANTONIO H. ROMANO. Control of isocitratase formation in Rhizopus nigricans. J. Bacteriol. 87:156–161. 1964.—A fumaric acid-producing strain of Rhizopus nigricans was found to produce a fair level of isocitratase in a casein hydrolysate medium. Glucose repressed enzyme formation. When glucose was utilized during growth, there was a relief of repression, and enzyme synthesis was resumed at a rate equivalent to that found in nonrepressed cells. Zinc stimulated isocitratase formation in glucose-repressed cultures by stimulating growth and glucose utilization, thereby decreasing accumulation of repressor metabolites derived from glucose. The effectiveness of acetate as an inducer was greater on glucose-repressed cells than on nonrepressed cells; cells grown in the presence of glucose formed higher levels of isocitratase when subsequently replaced with an acetate-containing inductive medium than did cells grown without glucose. Moreover, addition of 2 ppm of Zn⁺⁺ during the inductive replacement phase resulted in a twofold increase in isocitratase formation. The hypothesis is submitted that Zn⁺⁺ exerts its action by stimulating ribonucleic acid (RNA) synthesis, thereby facilitating the formation of a specific RNA during induction. Preliminary evidence implicating Zn⁺⁺ in the stimulation of RNA synthesis in this organism is presented.