A-oxoglutarate

Glutamine then reacts with a-oxoglutarate to form 2 molecules of glutamic add. This reaction is catalysed by glutamate oxoglutamate aminotransferase (GOGAT) and can be written as ... 

Other bacteria such as E. coli assimilate ammonia by incorporating it directly into a-oxoglutarate in a reaction catalysed by glutamate dehydrogenase (GDH). This reaction can be written as... 

GOGAT would otherwise compete with GDH for a-oxoglutarate ... 

The correct answer is 2). Both GDH and GOGAT use a-oxoglutarate as a substrate. GOGAT deletion ensures a-oxoglutarate is directed only through the GDH step. 

Table 5.1 Example of organic acids produced commercially by micro-organisms organic adds considered in this chapter are labelled with. A related add, a-oxoglutaric acid, is easy to produce microbiologically but has no current end use succinic acid is produced chemically. Amino adds are beyond the scope of this chapter.

Enzymes a) citrate synthase b) aconitase c) isocitrate dehydrogenase d) a-oxoglutarate dehydrogenase e) succiny CoA synthetase f) succinate dehydrogenase g) fumarase h) malate dehydrogenase i) nucleoside diphosphokinase. 

Figure 5.3 Major control points of glycolysis and the TCA cycle. Enzymes I, hexokinase II, phosphofructokinase III, pyruvate kinase IV, pyruvate dehydrogenase V, citrate synthase VI, aconitase VII, isocitrate dehydrogenase VIII, a-oxoglutarate dehydrogenase.

The diagram looks very promising in terms of citric acid formation in that a-oxoglutarate dehydrogenase is inactive, isodtrate dehydrogenase has veiy low activity and aconitase equilibrates 90% towards dtric add. 

The product is 2-oxoglutarate, sometimes referred to as a-oxoglutarate or a-ketoglutarate. Note specifically that we have just lost one of the carbon atoms. Oxaloacetate (a C4 compound) reacted with acetyl-CoA (C2) to give citrate (Cg), and this reaction... 

Tissues of the mammalian central nervous system contain a pyridoxal phosphate-dependent glutamate decarboxylase that catalyzes conversion of Glu to y-aminobutyrate (GABA), an inhibitory synaptic transmitter. GABA is degraded by trans-imination with a-oxoglutarate as the acceptor to yield succinic semialdehyde, which then is oxidized to succinate by an NAD-linked dehydrogenase. 

Abbreviations TCA tricarboxylic acid a-OG a-oxoglutarate PDC pyruvate dehydrogenase complex... 

In the widely used colorimetric assay of SGOT and SGPT (R2), serum is incubated at 37 °G with phosphate-buffered L-aspartate/a-oxoglutarate or DL-alanine/a-oxoglutarate, respectively, the reaction terminated after a definite interval by addition of 2,4-dinitrophenylhydrazine in dilute HCl, and after a period at room temperature the hydrazones of oxalace-tate or pyruvate so formed are treated with dilute alkali and the optical density measured against water at 505 mp the results are read from standard curves of optical density against transaminase activity. 

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