Nitrogen, following its initial assimilation into glutamine and glutamate can be distributed to many other compounds by the action of aminotransferases.

The final step in the synthesis of several amino acids is a transamination of the 2-keto analogue of the amino acid. Glutamate is often the amino-donor substrate in biosynthetic reactions, with the result that 2-oxoglutarate will be a product.

2-Oxoglutarate is a substrate required for nitrogen assimilation by both the GDH and GS/GOGAT pathways. Glutamate-utilizing transaminases therefore regenerate the carbon precursor needed for ammonia assimilation.

Regeneration of 2-oxoglutarate may permit assimilation to continue in the absence of net 2-oxoglutarate synthesis, as long as glutamate is not utilized by other reactions.

Somerville SC, Ogren WL 1983 An Arabidopsis thaliana mutant defective in chloroplast dicarboxylate transport. Proc. Natl. Acad. Sci. USA 80: 1290-1294.

Woo KC, Flugge UI, Heldt HW 1987 A two-translocator model for the transport of 2-oxoglutarate and glutamate in chloroplasts during ammonia assimilation in the light. Plant Physiol. 84: 624-632.