2-Oxoglutarate reductive amination

D. Mandler and 1. Willner, Photosensitized NAD(P)H regeneration systems application in the reduction of butan-2-one, pyruvic, and acetoacetic acids and in the reductive amination of pyruvic and oxoglutaric acids to amino acids,... 

This has obvious advantages over the process seen for glutamate synthesis via the reductive amination of 2-oxoglutarate, in that it no longer requires the intervention of free ammonia. We thus have the situation that some organisms are able to carry out the fixation of ammonia via reductive amination, whereas others manipulate via transamination the amino acid structures obtained from protein in the diet. 

The two transamination steps in the pathways may be linked, as indicated in Fig. 17-5, to form a complete cycle that parallels the citric acid cycle but in which 2-oxoglutarate is oxidized to succinate via glutamate and y-aminobutyrate. No thiamin diphosphate is required, but 2-oxoglutarate is reductively aminated to glutamate. The cycle is sometimes called the y-aminobutyrate shunt, and it plays a significant role in the overall oxidative processes of brain tissue. 

More specific labelling may be obtained in a biosynthetic process using enzymic methods of synthesis. The preparation of amino acids by the reductive amination of 2-keto acids is well known. Indeed, the synthesis of N-labelled amino acids by this route is among the earliest literature on the preparation of compounds labelled with stable isotopes [73], Such reductions can be carried out enzymically and L - [a- N] glutamic acid has been prepared in good yield from 2-oxoglutaric acid and N-labelled ammonium chloride in the presence of reduced nicotinamide adenine dinucleotide phosphate [74],... 

Two different routes for the biosynthesis of L-lysine are known in microorganisms. The a-aminoadipate route (AA), of which two variants are known, which start from 2-oxoglutarate and acetyl-CoA [23]. The three variants of the diaminopime-late route (DAP), which starts from L-aspartate, can be distinguished by their use of either succinylated or acetylated intermediates or by direct reductive amination of tetrahydropicolinate [24]. 

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