Catalytic and Molecular Aspects of the Functioning of Glutamate-Dehydrogenase Isoforms in Corn Zea mays L.

The dynamics of the activity of glutamate dehydrogenase (GDH, EC 1.4.1.2) during germination in corn leaves and scutes has been studied. It was found that changes in its activity are due to biochemical and molecular aspects of enzyme functioning. This was confirmed in a study of the relative level of transcripts of the gdh-1 and gdh-2 genes, which encode GDH subunits. It was shown that this enzyme in leaves is mainly localized in mitochondria (86.54%) and, to a lesser extent, cytosol (9.53%) and chloroplasts (3.92%). Four-stage purification made it possible to isolate three GDH enzyme preparations from corn leaves with different purification levels. One form (GDH1) was purified to a specific enzyme-preparation activity of 195 U/mg protein with a purification rate of 98 times and a yield of 8%. The second form (GDH2) was obtained with a specific activity of 166 U/mg protein, a purification rate of 83 times, and a yield of 32%. The GDH3 preparation had a specific activity of 122.2 U/mg protein, a purification rate of 61 times, and a yield of 21%. The pH optimum was determined from the amination reaction. The optimal pH values are 7.5 for GDH1 and 7.0 and 8.5 for GDH2 and GDH3, respectively. The obtained GDH isoforms have different Km values for 2-oxoglutarate: 0.34 mM for GDH1 and 0.6 mM and 0.22 mM, respectively, for GDH2 and GDH3.