2-Oxoglutarate from glutamate

The 2-oxoglutarate produced is recycled for transamination or may enter the TCA cycle. The ammonia liberated by oxidative deamination is used to form glutamine (from glutamate, catalysed by glutamine synthase) prior to export from the muscle cell ... 

The 2-oxoglutarate/L-glutamate couple serves as one amino group acceptor and donor pair in all amino-transfer reactions the specificity of the individual enzymes derives from the particular amino acid that serves as the other donor of an amino group. Thus AST catalyzes the reaction. 

Any oxaloacetate or 2-oxoglutarate removed from the TCA cycle must be replaced. Pyruvate is converted by pyruvate carboxylase to oxaloacetate, which can then enter the TCA cycle to yield 2-oxoglutarate. Also 2-oxoglutarate can be produced from glutamate and glutamine by transaminases. 

The 5 phosphoribosyl-l-pyrophosphate required for purine synthesis is obtained from ATP and ribose-5-phosphate by reaction (11.39). Glutamine, which is also required, is obtained from glutamic acid by reaction (11.44), and the latter is obtained from a - oxoglutaric acid by reaction (11.124). The last reaction links the Krebs cycle with amino acid metabolism. 

Fig. 13.4 Impact of change in activities of ICDH, GDH and ODHC on metabolic flux redistribution at the 2-oxoglutarate branch in C glutamicum. Glucose was used as a carbon source in this experiment. Input flux to 2-oxoglutarate from isocitrate was normalized to 100, and redistributed fluxes to succinyl-CoA and glutamate from 2-oxoglutarate are shown...

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