The Regulation of Synthesis of Krebs Cycle Enzymes in Neurospora by Catabolite and End Product Repression

Krebs cycle enzymes were repressed in Neurospora during growth on sucrose as carbon source compared with growth on acetate. In mitochondrial, cytochrome‐deficient strains grown on sucrose, this glucose or catabolite repression was reduced. In mutant strains in which protein synthesis and mitochondrial respiration were inhibited, catabolite repression was enhanced. These data support the hypothesis that ATP or the cellular energy level is involved in catabolite repression. The interrelationships between energy metabolism, the energy distribution in the cell and catabolite repression are discussed. The addition of casamino acids to a culture growing on sucrose or acetate, did not cause repression of any of the Krebs cycle enzymes measured, in spite of the fact that many of the constituent amino acids can be considered as biosynthetic products of the Krebs cycle.