2-ketoglutaric

There are several 2-ketoglutarate anaerobic oxidoreductases, for example, in Thauera aro-matica (Dorner and Boll 2002) and Azoarcus evansii (Ebenau-Jehle et al. 2003). Their role in the metabolism of arene carboxylates is discussed in Chapter 8, Part 3. 

Pyridine-4-carboxylate is hydroxylated by Mycobacterium sp. strain INAl to 2,6-dihydroxypyridine-4-carboxylate. Two different hydroxylation enzymes were involved and were apparently Mo-dependent (Kretzer and Andreesen 1991). The formation of 2-ketoglutarate can, however, be rationalized equally as (3-oxidation to hexahydropyridine-2,3,6-trione-4-carboxy-CoA ester followed by hydrolysis. 

Unusual 2-ketoglutarate-dependent dioxygenations have been found in the yeast Rhodotorula glutinis ... 

Nature uses enantioselective transfer hydrogenation to reduce metabolites, for example pyruvate to give (S)-lactic acid and 2-ketoglutarate to give (S)-2-hydroxy -glutarate. The reaction is reversible and the equilibrium position depends on the concentration of the species. The enzyme catalysts are named dehydrogenases, and they employ a soluble cofactor or hydride acceptor called NAD(P) in its oxi-... 

Schousboe, A., Wu, J. Y., and Roberts, E. (1973) Purification and characterization of the 4-aminobutyrate-2,ketoglutarate transaminase from mouse brain. Biochemistry 12,2868-2873. 

This enzyme [EC 2.6.1.2], also known as glutamic-pyruvic transaminase and glutamic-alanine transaminase, catalyzes the pyridoxal-phosphate-dependent reaction of alanine with 2-ketoglutarate, resulting on the production of pyruvate and glutamate. 2-Aminobutanoate will also react, albeit slowly. There is another alanine aminotransferase [EC 2.6.1.12], better known as alanine-oxo-acid aminotransferase, which catalyzes the pyridoxal-phosphate-dependent reaction of alanine and a 2-keto acid to generate pyruvate and an amino acid. See also Alanine Glyoxylate Aminotransferase... 

This enzyme [EC 1.14.11.1], also known as y-butyrobe-taine, 2-ketoglutarate dioxygenase, catalyzes the reaction of 4-trimethylammoniobutanoate with S-keto-glutarate (or, 2-oxoglutarate) and dioxygen to yield 3-hydroxy-4-trimethylammoniobutanoate, succinate, and carbon dioxide. Both iron ions and ascorbate are needed as cofactors. 

Figure 2. Alternative enzymatic routing for L-phenylalanine biosynthesis. Dehydration followed by transamination defines the phenylpyruvate route, whereas the reverse order of reactions defines the arogenate route. Abbreviations GLU, L-glutamate aKG, 2-ketoglutarate.

Keratinocytes, cosmetics, 613 a-Ketoalkyl radicals, 252 y-Ketoalkyl radicals, 252 of-Keto esters, benzylic oxidation, 518 2-Ketoglutarate, hydrogen peroxide determination, 655... 

CoA labeled with 14C (radioactive carbon) at the carboxyl group, CH3—14C—SCoA, into the citric acid cycle, the 2-oxopentanedioate acid (2-ketoglutarate) formed in the fourth step of the cycle would have all of the 14C in the carboxylate group farthest away from the ketone carbonyl group. For some years, this result was used to argue that citric acid itself could not be an intermediate in the formation of 2-oxopentanedioate. Review Section 19-8 and explain how, in stereospecific enzyme-induced reactions, citric acid could be an intermediate in the formation of 2-oxopentanedioate even if the 14C would not appear equally in both carboxylic carbons of the product. 

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