Biochemistry of Amino Acids - A. Majster 1961

General Biochemistry and Physiology of Amino Acid Metabolism
Oxidative Deamination
L-Glutamate Dehydrogenase

Reversible deamination of glutamic acid is of paramount importance in METABOLISM. In mammals and many other species, this reaction serves as one of the primary Mechanisms for the interconversion of $\alpha$-amino nitrogen and ammonia. Glutamate dehydrogenase is widely distributed, having been found in plants [155–157], animals [158, 159], and microorganisms [155, 160, 161]. The enzyme is detected in almost all mammalian Tissues, being most active in The Liver and Kidneys. The dehydrogenation of glutamic acid can be represented as follows:

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This reaction is similar to those catalyzed by general amino acid oxidases; it is hypothesized that an imino acid is formed as an intermediate product. The action of glutamate dehydrogenase from Higher Plants and most animal tissues involves diphosphopyridine nucleotide (DPN) as a coenzyme. The enzyme present in the liver Functions with the participation of both di- and triphosphopyridine nucleotide (TPN); however, under certain conditions, the TPN-dependent reaction proceeds at a lower rate [162]. For example, The rate of Oxidation of reduced triphosphopyridine nucleotide in tissue may be limited by a shortage of TPN-cytochrome reductase [163]. Glutamate dehydrogenases from Yeast and Escherichia coli are strictly specific for TPN [160, 161].

Bovine liver glutamate dehydrogenase has been obtained in crystalline form by two Methods [164, 165]. The enzyme contains zinc [166]. The equilibrium position of the reaction favors The formation of glutamic acid, and under appropriate conditions, the enzyme can be used to prepare N¹⁵-glutamic acid from $\alpha$-ketoglutarate and labeled ammonia.

Glutamate dehydrogenase is strictly specific for L-glutamic acid; glutamine, aspartic acid, $\alpha$-methylglutamic and y-methylglutamic acids, and other glutamic acid derivatives are not dehydrogenated by this enzyme.