GOGAT

GOGAT, short for glutamate synthase, is an enzyme that catalyzes the transfer of the amide group from glutamine to 2-oxoglutarate to form two molecules of glutamate. It functions as a key component of the GS-GOGAT cycle, which is a major pathway for assimilating inorganic nitrogen into organic molecules in many bacteria, fungi, and plants. There are two primary forms that differ in their electron donors: a ferredoxin-dependent GOGAT (Fd-GOGAT), which uses reduced ferredoxin, and a NADH- or NADPH-dependent GOGAT, which uses NADH or NADPH. Fd-GOGAT is common in plants and photosynthetic microorganisms, while NADH-GOGAT is found in many soil bacteria and some archaea, often as a heterodimer formed by the GltB and GltD subunits.

The reaction can be summarized as: L-glutamine + 2-oxoglutarate + reducing equivalent -> 2 L-glutamate + oxidized donor. The net effect of the GS-GOGAT cycle is the incorporation of ammonia into an amino acid pool, providing a mechanism for ammonium assimilation under varying environmental conditions.

In plants, Fd-GOGAT operates in chloroplasts alongside plastidic glutamine synthetase (GS2) and participates in photorespiratory nitrogen metabolism and general nitrogen assimilation. In microorganisms, GOGAT supports growth under ammonium limitation and is subject to regulation by nitrogen status. GOGAT is a focus of research on crop nitrogen-use efficiency and microbial nitrogen metabolism.