Effect of Glucose, Galactose, and Different Nitrogen‐Sources on the Activity of Yeast Glutamate Dehydrogenase (NAD and NADP‐Linked) from Normal Strain and Impaired Respiration Mutant

Abstract

The activity of glutamate dehydrogenase from baker's yeast grown in various concentrations of glucose and galactose has been studied. The yeasts were grown under aerobic and anaerobic conditions and harvested after 24 h. Experiments have also been carried out with impaired respiration mutants induced by trypaflavine (“petite mutante”). A comparison of the NAD‐and NADP‐glutamate dehydrogenase activities of normal and impaired respiration yeasts is reported. The repression of the aminating reaction of the glutamate dehydrogenase by ammonia has also been investigated. When the normal cells are grown in a medium which contains 0.3% sugar the main activity of the aminating reaction is glutamate dehydrogenase NADH‐linked. When grown anaerobically (with glucose or galactose) the activity of the NADH‐enzyme decreases while that of the glutamate dehydrogenase‐NADPH increases. In the cells grown anaerobically and in those with impaired respiration, there is no significant activity of glutamate dehydrogenase‐NADH in any case. In impaired respiration cells, the levels of activity are similar to those of normal cells grown anaerobically. With higher concentrations of sugars the glutamate dehydrogenase‐NADH is strongly repressed, while there is a simultaneous increase of the glutamate dehydrogenase‐NADPH. Ammonia acts as a repressor of the glutamate dehydrogenase activity in normal cells. In “petite mutante” the greatest activity of the glutamate dehydrogenase‐NADPH was found in cultures with glutamate and alanine as nitrogen source; in all cases, the presence of ammonia either alone or with another nitrogen source represses activity. Copyright © 1970, Wiley Blackwell. All rights reserved