Ammonium ion-dependent isomerization of glutamate dehydrogenase in relation to glutamate synthesis in maize
The glutamate dehydrogenase [GDH, EC 188.8.131.52] from maize seeds that were germinated in the presence of different concentrations of NH4Cl had charge isomers in the pH 5.8-7.5 range. In a three-phase process, different NH4Cl concentrations sequentially altered the binomial distribution of the GDH isoenzyme population. The first phase of GDH isomerization was by low (< 2 mM); the second was by medium (2-58 mM); and the third was by high ( >58 mM) NH4Cl concentrations. Ammonium ion isomerized the GDH by regulating the hexameric subunit assembly reaction. The isomerization was abolished by methionine sulphoximine. The GDH isoenzyme population distribution that was induced by 25 mM NH4Cl closely approached the theoretical binomial distribution, and it also gave the highest GDH activity. An analysis of the free amino acids of maize seeds, and comparison of the activities of GDH and glutamate synthase (GOGAT), in each of the three phases of GDH isomerization, showed that GDH was 25% more efficient than GOGAT in the synthesis of l-Glu. © 1995.
Osuji, G., & Madu, W. (1995). Ammonium ion-dependent isomerization of glutamate dehydrogenase in relation to glutamate synthesis in maize. Phytochemistry, 39 (3), 495-503. https://doi.org/10.1016/0031-9422(94)00976-Z