2-Oxoglutarate synthase

This enzyme [EC 1.2.7.3], also called 2-oxoglutarate synthase, catalyzes the reversible reaction of a-ketoglutarate (or, 2-oxoglutarate) with coenzyme A and oxidized ferredoxin to produce succinyl-CoA, carbon dioxide, and reduced ferredoxin. 

Reductive citric acid cycle 5 3 NAD(P)H, 1 unknown donor", 2 ferredoxin 2-Oxoglutarate synthase Isocitrate dehydrogenase6 Pyruvate synthase PEP carboxylase C02 C02 C02 HCOJ Acetyl-CoA, pyruvate, PEP, oxaloacetate, succinyl-CoA, 2-oxoglutarate 2-Oxoglutarate synthase, ATP-citrate lyase... 

Three modifications of the conventional oxidative citric acid cycle are needed, which substitute irreversible enzyme steps. Succinate dehydrogenase is replaced by fumarate reductase, 2-oxoglutarate dehydrogenase by ferredoxin-dependent 2-oxoglutarate oxidoreductase (2-oxoglutarate synthase), and citrate synthase by ATP-citrate lyase [3, 16] it should be noted that the carboxylases of the cycle catalyze the reductive carboxylation reactions. There are variants of the ATP-driven cleavage of citrate as well as of isocitrate formation [7]. The reductive citric acid... 

Figure 3.2 Reductive citric acid cycle, ffi, ATP-citrate lyase 2-oxoglutarate ferredoxin oxidoreductase (2-oxoglutarate synthase)

Purification and characterization of 2-oxoglutarate synthase (2-Oxoglutarate ferredoxin oxidoreductase (OGOR)) [10]... 

Enzymes a) citrate synthase b) aconitase c) isocitrate dehydrogenase d) a-oxoglutarate dehydrogenase e) succiny CoA synthetase f) succinate dehydrogenase g) fumarase h) malate dehydrogenase i) nucleoside diphosphokinase. 

Figure 5.3 Major control points of glycolysis and the TCA cycle. Enzymes I, hexokinase II, phosphofructokinase III, pyruvate kinase IV, pyruvate dehydrogenase V, citrate synthase VI, aconitase VII, isocitrate dehydrogenase VIII, a-oxoglutarate dehydrogenase.

Turnbull JJ, Nakajima J, Welford RW, Yamazaki M, Saito K and Schofield CJ. 2004. Mechanistic studies on three 2-oxoglutarate-dependent oxygenases of flavonoid biosynthesis anthocyanidin synthase, flavonol synthase, and flavanone 33-hydroxylase. J Biol Chem 279 1206-1216. 

The 2-oxoglutarate produced is recycled for transamination or may enter the TCA cycle. The ammonia liberated by oxidative deamination is used to form glutamine (from glutamate, catalysed by glutamine synthase) prior to export from the muscle cell ... 

Figure 9.2 Summary of reactions of the Krebs cycle. The names of the enzymes are dtrate synthase, aconitase, isodtrate dehydrogenase (there are two enzymes, one ubTizes NAD as the cofactor, the other NADPT it is assumed that the NAD -specific enzyme is that involved in the cycle), oxoglutarate dehydrogenase, sucdnyl CoA synthetase, succinate dehydrogenase, fumarate hydratase, malate dehydrogenase.

Flavone synthase (FNS EC 1.14.11.22) introduces a double bond between C2 and C3 of a flavanone to produce the corresponding flavone. This activity was initially identified in parsley cell suspension cultures and subsequently shown to be encoded by a 2-oxoglutarate-dependent dioxygenase [67, 78, 79], This enzyme, now known as FNS-I, appears to have very limited distribution. To date, it has only been identified in the Apiaceae family (Umbellifers). The more widely occurring FNS-II (CYP93B) was initially identified from snapdragon (Antirrhinum majus) flowers [80] and was subsequently shown to be a P450 enzyme. FNS-I, FNS-II, and the various roles flavones play in plant species have recently been reviewed by Martens and Mithofer [81], Subsequent to this review, Yu et al. [82] demonstrated that the characteristic lack of natural accumulation of flavones in Brassicaceae could not be overcome in A. thaliana even by overexpression of recombinant parsley FNS-I. 

Flavonol synthase (FLS E.C.l.14.11.23) catalyzes the committed step in the production of fiavonols by introduction of a double bond between C2 and C3 of the corresponding dihydroflavonols. Like E3H, ELS has been described as a 2-oxoglutatarate-dependent dioxygenase based on its cofactor requirements for 2-oxoglutarate, Fe, and ascorbate. FLS was initially identified in enzyme preparations from illuminated parsley cell suspension cultures [67]. Subsequently, FLS was characterized from the flower buds of Matthiola incana and carnation (Dianthus caryophyllus L.), and it was suggested that there was regulation between flavonol and anthocyanidin biosynthesis [83, 84]. 

Halbwirth H, Fischer TC, Schlangen K, Rademacher W, Schleifer K, Forkmann G, Stitch K (2006) Screening for inhibitors of 2-oxoglutarate-dependent dioxygenases flavanone 3-hydroxylase and flavonol synthase. Plant Sd 171 194-205... 

Saito K, Kobayashi M, Gong Z, Tanaka Y, Yamazaki M (1999) Direct evidence for anthocyanidin synthase as a 2-oxoglutarate-dependent oxygenase molecular cloning and functional expression of cDNA from a red form of Perilla frutescens. Plant J 17(2) 181-189... 

Glutamate synthase (NADPH) [EC 1.4.1.13], an iron-sulfur flavoprotein, catalyzes the reaction of L-glutamine with a-ketoglutarate (or, 2-oxoglutarate) and NADPH to produce NADP+ and two glutamate molecules. Ammonia can act as the nitrogen donor substrate instead of L-glutamine, albeit weaker. 

Britsch, L., Purification and characterization of flavone synthase 1, a 2-oxoglutarate-dependent desaturase. Arch. Biochem. Biophys., 282, 152, 1990. 

J Cortes, IF Martin, JM Castro, L Laiz, P Liras. Purification and characterization of a 2-oxoglutarate linked ATP-independent deacetoxycephalosporin C synthase of Streptomyces lactamdurans. J Gen Microbiol 133 3165-3174, 1987. 

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