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Plant and Cell Physiology, 1962, Vol. 3, No. 3 293-307
© 1962

Article

FLAVOPROTEINS IN THE LEAVES OF HIGHER PLANTS CATALYZING THE OXIDATION OF L-GLUTAMATE

AKIRA TSUKAMOTO

The Department of Biology, Faculty of Science, Ochanomizu University Tokyo

  1. Two forms of enzyme capable of catalyzing the oxidation of L-glutamate (and L-aspartate) were isolated from the leaves of spinach and separated from each other by column-chromatographic purification on calcium phosphate and anion exchangers. They were distinguished as GD1 (L-glutamate dehydrogenase 1) and GD2 (L-glutamate dehydrogenase 2). The purification procedures and some fundamental properties of the partially purified enzymes were investigated.
  2. It was discovered that the enzymes did not require any cofactor, i e., neither dialysis nor precipitation with ammonium sulfate caused a fall in enzyme activities and the addition of DPN and TPN to the reaction mixture did not accelerate the reaction rate
  3. From the results of spectroscopic investigation GD1 and GD2 were shown to be flavoproteins, although their prosthetic group has not yet been identified The activity of GD1 was enhanced by the addition of FAD or FMN, while GD2 was not accelerated by these factors.
  4. The characteristics of the two enzymes including substrate specificity, MICHAELIS constant, optimum pH of the reaction and specificity for electron acceptors were compared.
  5. From the stoichiometric study of the oxidation of L-glutamate with these enzymes, it was confirmed that the reaction is represented by the following equation: L-glutamate+oxidized dye+h2oFormula
  6. Among various inhibitors tested, molecular oxygen which could function as electron acceptor of L-glutamate oxidation in the presence of GD1 was found to cause a strong inhibition upon the same reaction with TTC as el acceptor. The inhibition was confirmed to be due to hydrogen peroxide produced as a result of the aerobic oxidation of L-glutamate.

(Received July 25, 1962; )
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