Re-assessment of ammonium-ion affinities of NADP-specific glutamate dehydrogenases. Activation of the Neurospora crassa enzyme by ammonium and rubidium ions.
The NADP-specific glutamate dehydrogenase of Neurospora crassa shows complex interactions with NH4+ ions, characterized by biphasic downwardly convex double-reciprocal plots. These kinetics are explained by the action of NH4+ both as a substrate and, acting at a separate cation-binding site, as an activator. Rb+ ions, and to a smaller extent other univalent cations, also activate by acting as analogues of NH4+. Previous failure to recognize this effect, which probably also occurs in homologous enzymes from some other species, has led to significant overestimates in published reports of the Km for NH4+ of some NADP-specific glutamate dehydrogenases.
D000643:Ammonium Chloride / Q000494:pharmacology*; D002412:Cations / Q000494:pharmacology; D002708:Chlorella / Q000201:enzymology; D004789:Enzyme Activation / Q000187:drug effects; D005969:Glutamate Dehydrogenase / Q000378:metabolism*; D007700:Kinetics; D009249:NADP / Q000494:pharmacology; D009491:Neurospora / Q000201:enzymology*; D009492:Neurospora crassa / Q000201:enzymology*; D012413:Rubidium / Q000494:pharmacology*
D002412:Cations; D000643:Ammonium Chloride; D009249:NADP; D005969:Glutamate Dehydrogenase; D012413:Rubidium