Changes in the activities of respiratory enzymes during the aerobic growth of yeast on different carbon sources.

1. Unlike yeast cells grown on glucose (0.9%), cells grown on galactose aerobically or anaerobically as well as cells grown on very low glucose concentrations (0.09%) have been found to possess mitochondria. 2. Synthesis of respiratory enzymes was less in the presence of glucose than galactose. When either sugar was consumed, synthesis of these enzymes increased. 3. A possible mechanism is suggested for the repression of mitochondrial formation by glucose by means of a ;high-energy' substance easily derived from glucose.