Abstract
10nM cyclic AMP causes a slow lifting of catabolite repression of a-glucosidase (but not invertase), in the presence of 2% glucose, in yeast protoplasts but not in whole yeast. alpha-Glucosidase is partially protected in vivo from loss under deadaptation conditions by maltose. Protection in vitro by cyclic AMP or maltose is shown, against chemical inhibitors or heat. The concentration of intracellular cyclic AMP was found to be low under high glucose conditions and to parallel the appearance of cytochrome P-450 (but not its loss). In agreement with this, the cytochrome P-450 concentration is high in high glucose media (5-20%): and cytochrome a+a[3] formation is repressed as expected. Maximal levels of cytochrome P-450 are reached at the end of the growth phase (40 hours of culture) in high glucose media. Rapid disappearance of the enzyme occurs after this, but the cyclic AMP level did not rise, despite the rise in cytochrome a+a[3] level. Cytochrome P-450 is produced rapidly during early phase of growth, up to 17 hours in 1% and 2.5% glucose media (none is produced in 0.1% glucose medium where cyclic AMP levels are high). The cytochrome P-450 subsequently disappears from the yeast while the appearance of cytochrome a+a[3] can now be observed. Cyclic AMP added to the yeast protoplast can prevent the accumulation of cytochrome P-450 in 20% glucose medium, where it is otherwise formed. Conversely, induction of cytochrome P-450 by cyclic GMP has been demonstrated in yeast protoplasts. Sodium phenobarbital, at 0.2%, causes the maximal accumulation of cytochrome P-450 in yeast growing in 0. 5% glucose medium. Also, various antimitochondrial drugs had been studied in relation to the accumulation of cytochrome P-450. The optimal conditions of cytochrome P-450 production in yeast have been determined in continuous culture. The opposing behaviour of cyclic AMP and cyclic GMP in the regulation of these yeast enzymes is discussed.