title: Regulation by ammonium of glutamate dehydrogenase (NADP+) from Saccharomyces cerevisiae.
abstract: The activity of glutamate dehydrogenase (NADP+) (EC 1.4.1.4; NADP-GDH) of Saccharomyces cerevisiae is decreased under conditions in which intracellular ammonia concentrations increases. A high internal ammonia concentration can be obtained (a) by increasing the ammonium sulphate concentration in the culture medium, and (b) by growing the yeast either in acetate + ammonia media, where the pH of the medium rises during growth, or in heavily buffered glucose + ammonia media at pH 7.5. Under these conditions cellular oxoglutarate concentrations do not vary and changes in NADP-GDH activity appear to provide a constant rate of oxoglutarate utilization. The following results suggest that the decrease in NADP-GDH activity in ammonia-accumulating yeast cells is brought about by repression of synthesis: (i) after a shift to high ammonium sulphate concentrations, the number of units of activity per cell decreased as the inverse of cell doubling; and (ii) the rate of degradation of labelled NADP-GDH was essentially the same in ammonia-accumulating yeast cells and in controls, whereas the synthesis constant was much lower in the ammonia-accumulating cells than in the controls.
mesh_terms: D000085:Acetates / Q000494:pharmacology; D000641:Ammonia / Q000494:pharmacology*; D004794:Enzyme Repression / Q000187:drug effects; D005969:Glutamate Dehydrogenase / Q000096:biosynthesis*; D018086:Glutamate Dehydrogenase (NADP+); D006863:Hydrogen-Ion Concentration; D012441:Saccharomyces cerevisiae / Q000201:enzymology*
chemical_list: D000085:Acetates; D000641:Ammonia; D005969:Glutamate Dehydrogenase; D018086:Glutamate Dehydrogenase (NADP+)