Biochemistry - Chemical Reactions in Living Cells, Volume 2 - D. Metzler 1980

Coenzymes — special naturally occurring specialized reagents
Pyridine nucleotide coenzymes and dehydrogenases
Glutamate dehydrogenase

The reduction of the Schiff base (Table 8-3, reaction B) is catalyzed by glutamate dehydrogenase (Chap. 14, Sec. B,1). The bovine enzyme is a large hexameric protein composed of subunits with a Molecular Weight of approximately 56,000. Each subunit consists of 500 amino acid residues, The sequence of which is already known [83]. The sodium borohydride reduction of the glutamate dehydrogenase-enzyme-substrate complex with α-ketoglutarate indicates The formation of a Schiff base with Lys-126. This seems peculiar, since for reduction to glutamate, ketoglutarate must react with ammonia rather than with a Lysine side chain. It is possible that ammonia adds to the ketoglutarate-lysine Schiff base, followed by transaldimination (Sec. D, 6, b) to form a Schiff base with ammonia. Alternatively, the NH3 adduct may be reduced via substitution, with the simultaneous displacement of a hydride ion from an NADH or NADPH molecule [Eq. (8-40)]

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It is also possible that an imidazole group is present in the Active Site of the enzyme [84].

1) See also a later review by Lazdunski [Lazdunski M. (1974), Progress in Bioorganic Chemistry (Kaiser E. T. and Kezdy F. J., eds.), v. 3, p. 81]. — Transl. note.



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