Regulation of Two Soluble Forms of Brain Glutamate Dehydrogenase Isoproteins by Leucine

  • Lee, Jong-Weon (Department of Parasitology and Institute of Tropical Medicine, Yonsei University College of Medicine) ;
  • Lee, Jong-Eun (Department of Anatomy, Yonsei University College of Medicine) ;
  • Choi, Soo-Young (Department of genetic Engineering, College of Natural Science, Hallym University) ;
  • Cho, Sung-Woo (Department of Biochemistry, College of Medicine, University of Ulsan)
  • 발행 : 1997.09.30

초록

The stimulatory effects of leucine on the activities of two soluble forms of brain glutamate dehydrogenase isoproteins (GDH I and GDH II) have been studied at various conditions. There were significant differences between GDH I and GDH II in their sensitivities to the action of leucine. When the effects of varied leucine concentrations on GDH activities were studied in the direction of reductive amination of 2-oxoglutarate with NADPH as a coenzyme, a marked activation was observed for both isoproteins at leucine concentrations up to 10 mM, whereas both isoproteins showed activation to a lesser extent with NADH as a coenzyme. The stimulatory effects of leucine on GDH activities in the direction of the oxidative deamination of glutamate were also observed, but to a much lesser extent. Leucine relieved the inhibition of GDH I by GTP and this resulted in an increase in the apparent activation by leucine in the presence of GTP. 2-Oxoglutarate was found to give rise to high substrate inhibition and leucine significantly reduced the substrate inhibition in the presence of $200\;{\mu}M$ NADH. Thus, the effects of leucine might be composed of a direct effect on the enzyme together with a relief of high substrate inhibition.

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