Question

Describe the central role of glutamate synthetase in nitrogen metabolism and the reason why its regulation should be so complex?

Answer 1

Glutamine is required in order to respond to nitrogen concentration however, glutamate plays no importance in determining the concentration of nitrogen but important for maintaining the osmoregulation the cells. Therefore, it is important to maintain the regulation of both glutamine and glutamate independent of each other which is quite complex.

Plant cells avoid ammonium toxicity by rapidly converting the ammonium generated from nitrate assimilation into amino acids. The conversion of ammonia into amino acid involves the sequential action of two enzymes glutamine synthetase and glutamate synthase. Glutamine synthetase combines ammonium ion with glutamate to form glutamine. This reaction requires ATP and divalent cations as a cofactor.

Glutamine is then back converted to glutamate by the transfer of the amide group to a molecule of ?-ketoglutarate. It is catalyzed by glutamate synthase and requires reducing potential in the form of NADP. Plants contain two types of glutamate synthase; one accepts electrons from NADH; the other accepts electrons from ferredoxin. The reaction will give two molecules of glutamate.