The citric acid cycle —also known as the Krebs cycle, Szent-Györgyi-Krebs cycle or the TCA cycle (tricarboxylic acid cycle)—is a series of chemical reactions to release stored energy through the oxidation of acetyl-CoA derived from carbohydrates, fats, and proteins. The Krebs cycle is used by organisms that respire (as opposed to organisms that ferment) to generate energy, either by anaerobic respiration or aerobic respiration. In addition, the cycle provides precursors of certain amino acids, as well as the reducing agent NADH, that are used in numerous other reactions. Its central importance to many biochemical pathways suggests that it was one of the earliest components of metabolism. Even though it is branded as a 'cycle', it is not necessary for metabolites to follow only one specific route; at least three alternative segments of the citric acid cycle have been recognized.
Substrate-level phosphorylation is a metabolism reaction that results in the production of ATP or GTP supported by the energy released from another high-energy bond that leads to phosphorylation of ADP or GDP to ATP or GTP (note that the reaction catalyzed by creatine kinase is not considered as "substrate-level phosphorylation"). This process uses some of the released chemical energy, the Gibbs free energy, to transfer a phosphoryl (PO3) group to ADP or GDP. Occurs in glycolysis and in the citric acid cycle.
Succinyl coenzyme A synthetase is an enzyme that catalyzes the reversible reaction of succinyl-CoA to succinate. The enzyme facilitates the coupling of this reaction to the formation of a nucleoside triphosphate molecule from an inorganic phosphate molecule and a nucleoside diphosphate molecule. It plays a key role as one of the catalysts involved in the citric acid cycle, a central pathway in cellular metabolism, and it is located within the mitochondrial matrix of a cell.
Phosphoribosylformylglycinamidine cyclo-ligase is the fifth enzyme in the de novo synthesis of purine nucleotides. It catalyzes the reaction to form 5-aminoimidazole ribotide (AIR) from formylglycinamidine-ribonucleotide FGAM. This reaction closes the ring and produces a 5-membered imidazole ring of the purine nucleus (AIR):
In enzymology, an acetate—CoA ligase (ADP-forming) is an enzyme that catalyzes the chemical reaction
Butyrate—CoA ligase, also known as xenobiotic/medium-chain fatty acid-ligase (XM-ligase), is an enzyme that catalyzes the chemical reaction:
In enzymology, a citrate—CoA ligase is an enzyme that catalyzes the chemical reaction
In enzymology, a D-alanine—D-alanine ligase is an enzyme that catalyzes the chemical reaction
In enzymology, a dethiobiotin synthase (EC 6.3.3.3) is an enzyme that catalyzes the chemical reaction
In enzymology, a dihydrofolate synthase is an enzyme that catalyzes the chemical reaction
In enzymology, a diphthine—ammonia ligase (EC 6.3.1.14, diphthamide synthase, diphthamide synthetase) is an enzyme that catalyzes the chemical reaction
In enzymology, a glutamate-putrescine ligase is an enzyme that catalyzes the chemical reaction
In enzymology, a glutarate—CoA ligase is an enzyme that catalyzes the chemical reaction
In enzymology, a glutathionylspermidine synthase is an enzyme that catalyzes the chemical reaction
In enzymology, a malate—CoA ligase is an enzyme that catalyzes the chemical reaction
In molecular biology, the protein domain SAICAR synthase is an enzyme which catalyses a reaction to create SAICAR. In enzymology, this enzyme is also known as phosphoribosylaminoimidazolesuccinocarboxamide synthase. It is an enzyme that catalyzes the chemical reaction
In enzymology, a succinate—CoA ligase (GDP-forming) is an enzyme that catalyzes the chemical reaction
In enzymology, a tetrahydrofolate synthase is an enzyme that catalyzes the chemical reaction
In enzymology, a UDP-N-acetylmuramate—L-alanine ligase is an enzyme that catalyzes the chemical reaction
Succinyl-CoA ligase [GDP-forming] subunit alpha, mitochondrial is an enzyme that in humans is encoded by the SUCLG1 gene.
