Succinyl CoA synthetase

Lsocitrate Dehydrogenase—The First Oxidadon in die Cycle m-Ketoglutarate Dehydrogenase—A Second Decarboxylation Succinyl-CoA Synthetase—A Substrate-Level Phosphoryladon Succinate Dehydrogenase—An Oxidadon Involving FAD... 

The mechanism of succinyl-CoA synthetase is postulated to involve displacement of CoA by phosphate, forming succinyl phosphate at the active site, followed by transfer of the phosphoryl group to an active-site histidine (making a phosphohistidine intermediate) and release of succinate. The phosphoryl moiety is then transferred to GDP to form GTP (Figure 20.13). This sequence of steps preserves the energy of the thioester bond of succinyl-CoA in a series of high-energy intermediates that lead to a molecule of ATP ... 

Succinyl-CoA is converted to succinate by the enzyme succinate thiokinase (succinyl-CoA synthetase). This is the only example in the citric acid cycle of substrate-level phosphorylation. Tissues in which glu-coneogenesis occurs (the hver and kidney) contain two isoenzymes of succinate thiokinase, one specific for GDP and the other for ADP. The GTP formed is used for the decarboxylation of oxaloacetate to phos-phoenolpymvate in gluconeogenesis and provides a regulatory hnk between citric acid cycle activity and the withdrawal of oxaloacetate for gluconeogenesis. Nongluconeogenic tissues have only the isoenzyme that uses ADP. 

The main source of GTP fot phosphoenolpytuvate catboxykinase inside the mitochondrion is the teaction of succinyl-CoA synthetase (Chaptet 16). This provides a hnk and hmit between cittic acid cycle activity and the extent of withdtawal of oxaloacetate fot gluconeogenesis. 

Brondijk THC, Durand R, van der Giezen M, et al. 1997. scsb, a cDNA encoding the hydrogenosomal beta subunit of succinyl-CoA synthetase from the anaerobic fungus Neocallimastix frontalis. Mol Gen Genet 253 315-23. 

Succinyl CoA synthetase (succinate thiokinase) catalyzes a substrate-level phosphorylation of GDP to GTP. 

The subsequent cleavage of the thio-ester succinylCoA into succinate and coenzyme A by succinic acid-CoA ligase (succinyl CoA synthetase, succinic thiokinase) is strongly exergonic and is used to synthesize a phosphoric acid anhydride bond ( substrate level phosphorylation , see p. 124). However, it is not ATP that is produced here as is otherwise usually the case, but instead guanosine triphosphate (CTP). However, GTP can be converted into ATP by a nucleoside diphosphate kinase (not shown). 

Succinyl-CoA synthetase (GDP) [EC 6.2.1.4], also known as succinate CoA ligase, catalyzes the reversible reaction of GTP with succinate and coenzyme A to produce GDP, succinyl-CoA, and orthophosphate. The nucleotide substrate can be replaced with ITP and itaconate can substitute for succinate. 

SERINE PALMITOYLTRANSFERASE SUCCINYL-CoA SYNTHETASE TRANSCARBOXYLASE VINYLACETYL-CoA ISOMERASE COENZYME Q (Ubiquinone)... 

SUCCINYL-CoA SYNTHETASE TUBULIN-GTR HYDROLYSIS VESICLE TRANSRORT IN CELLS GTP depletion,... 

SELENOPHOSPHATE SYNTHETASE STARCH PHOSPHORYLASE SUCCINYL-CoA SYNTHETASE SUCROSE PHOSPHORYLASE TUBULIN.TYROSINE LIGASE ORTHOPHOSPHATE CONTINUOUS ASSAY Orthovanadate,... 

SUCCINYL-CoA SYNTHETASE SUCCINYL-CoA SYNTHETASE O-Succinyl-L-homoserine,... 

Lahti CJ, Bradley PJ, Johnson PJ (1994) Molecular characterization of the alpha-subunit of Trichomonas vaginalis hydrogenosomal succinyl CoA synthetase. Mol Biochem Para-sitol 66 309-318... 

Succinyl coA synthetase, (1-subunit Neocallimastix sp. L2 MLANVTRSTSKAAPALASIAQTAQKRF LSV Brondijk et al. (1996)... 

Fig. 2 SDS-polyacrylamide gel electrophoresis of T. vaginalis hydrogenosomes purified by isopycnic centrifugation on a Percoll gradient. 1 PFOR 2 malic enzyme, 64-kDa hy-drogenase, and Cpn 60 3 succinyl CoA synthetase fi subunit 4 Hmp35 5 succinyl CoA synthetase a subunit 6 Hmp31 (ATP/ADP carrier) 7 adenylate kinase 8 thiol peroxidase. Well-resolved but unmarked bands mostly belong to malic enzyme fragments or unknown proteins. Proteins were identified by mass spectroscopy. The 12% gel is stained with Coomassie Brilliant Blue R 250 (authors original)...

Succinyl-CoA synthetase (SCS), also known as succinate thiokinase (STK) or succinate CoA ligase ( 6.2.1.4-5), is so far the only known hydrogenosomal enzyme directly involved in energy conservation. The protein catalyzes the reversible, substrate-level phosphorylation of ADP or GDP to the respective triphosphate at the expense of the high-energy thioester bond of succinyl-CoA. Succinate and CoA are released in the reaction. The I vaginalis enzyme... 

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