3] l-Glutamate dehydrogenase from bovine liver

Abstract

This chapter focuses on L-glutamate dehydrogenase derived from bovine liver. L-glutamate dehydrogenase is a pyridine nucleotide enzyme, which catalyzes the reversible oxidative deamination of L-glutamate to α-ketoglutarate and ammonia. While this enzyme is very widely distributed in nature, the mammalian forms constitute a more or less discrete class, all, for example, sharing the ability to use either NADP(H) or NAD(H) as coenzymes, along with a number of other common properties. This enzyme has a unique role in mammalian metabolism. The “reverse reaction” which it catalyzes is the only pathway by which ammonia can become bound to the α-carbon atom of an α-carboxylic acid in any mammalian tissue and thus constitutes the only source of de novo amino acid synthesis in such species. The bovine enzyme is characterized by three sets of properties: (1) a reversible concentration-dependent association to higher molecular weight forms; (2) the formation of tight ternary enzyme-reduced coenzyme-substrate (or product) ternary complexes whose rates of dissociation modulate the observed steady-state reaction rates; and (3) a wide variety of effects from the binding of any of a number of nucleotide modifiers. Because all these features interact with each other, the resulting behavior is much more complex than that of other pyridine nucleotide dehydrogenases.