Photosynthesis Research (2005) 83: 191–217 Ó Springer 2005 Review Glutamate synthase: structural, mechanistic and regulatory properties, and role in the amino acid metabolism Akira Suzuki1,* & David B. Knaff2 1Unite´ de Nutrition Azote´e des Plantes, Institut National de la Recherche Agronomique, Route de Saint-Cyr, 78026 Versailles cedex, France; 2Department of Chemistry and Biochemistry, Texas Tech University, P.O. Box 41061, Lubbock, TX 79409-1061, USA; *Author for correspondence (e-mail:
[email protected]; fax: +33-1-30833096) Received 28 June 2004; accepted in revised form 20 September 2004 Key words: ammonium assimilation, glutamate synthase, glutamine synthetase, higher plants, nitrogen metabolism Abstract Ammonium ion assimilation constitutes a central metabolic pathway in many organisms, and glutamate synthase, in concert with glutamine synthetase (GS, EC 6.3.1.2), plays the primary role of ammonium ion incorporation into glutamine and glutamate. Glutamate synthase occurs in three forms that can be dis- tinguished based on whether they use NADPH (NADPH-GOGAT, EC 1.4.1.13), NADH (NADH-GO- GAT, EC 1.4.1.14) or reduced ferredoxin (Fd-GOGAT, EC 1.4.7.1) as the electron donor for the (two- electron) conversion of L-glutamine plus 2-oxoglutarate to L-glutamate. The distribution of these three forms of glutamate synthase in different tissues is quite specific to the organism in question. Gene structures have been determined for Fd-, NADH- and NADPH-dependent glutamate synthases from different organisms, as shown by searches in nucleic acid sequence data banks. Fd-glutamate synthase contains two electron-carrying prosthetic groups, the redox properties of which are discussed.