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 biochemical reactions to release the energy stored in nutrients through the oxidation of acetyl-CoA derived from carbohydrates, fats, and proteins. The chemical energy released is available under the form of ATP. 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.
The enzyme citrate synthase E.C. 2.3.3.1 ] exists in nearly all living cells and stands as a pace-making enzyme in the first step of the citric acid cycle. Citrate synthase is localized within eukaryotic cells in the mitochondrial matrix, but is encoded by nuclear DNA rather than mitochondrial. It is synthesized using cytoplasmic ribosomes, then transported into the mitochondrial matrix.
In enzymology, a 5-hydroxypentanoate CoA-transferase is an enzyme that catalyzes the chemical reaction
In enzymology, an acetate CoA-transferase is an enzyme that catalyzes the chemical reaction
In enzymology, a citramalate CoA-transferase is an enzyme that catalyzes the chemical reaction
In enzymology, a glutaconate CoA-transferase is an enzyme that catalyzes the chemical reaction
In enzymology, a malonate CoA-transferase is an enzyme that catalyzes the chemical reaction
In enzymology, a propionate CoA-transferase is an enzyme that catalyzes the chemical reaction
The enzyme citrate (pro-3S)-lyase catalyzes the chemical reaction
The enzyme citryl-CoA lyase catalyzes the chemical reaction
In enzymology, a citrate—CoA ligase is an enzyme that catalyzes the chemical reaction
In enzymology, a [citrate (pro-3S)-lyase] ligase is an enzyme that catalyzes the chemical reaction
The enzyme citrate lyase deacetylase (EC 3.1.2.16) catalyzes the reaction
In enzymology, a 2-methylcitrate synthase (EC 2.3.3.5) is an enzyme that catalyzes the chemical reaction
ATP citrate synthase (also ATP citrate lyase (ACLY)) is an enzyme that in animals represents an important step in fatty acid biosynthesis. By converting citrate to acetyl-CoA, the enzyme links carbohydrate metabolism, which yields citrate as an intermediate, with fatty acid biosynthesis, which consumes acetyl-CoA. In plants, ATP citrate lyase generates cytosolic acetyl-CoA precursors of thousands of specialized metabolites, including waxes, sterols, and polyketides.
In enzymology, a citrate (Re)-synthase (EC 2.3.3.3) is an enzyme that catalyzes the chemical reaction
In enzymology, a deacetyl-[citrate-(pro-3S)-lyase] S-acetyltransferase (EC 2.3.1.49) is an enzyme that catalyzes the chemical reaction
In enzymology, a [acetyl-CoA carboxylase] kinase is an enzyme that catalyzes the chemical reaction
In molecular biology, the citrate synthase family of proteins includes the enzymes citrate synthase EC 2.3.3.1, and the related enzymes 2-methylcitrate synthase EC 2.3.3.5 and ATP citrate lyase EC 2.3.3.8.
Coenzyme A transferases (CoA-transferases) are transferase enzymes that catalyze the transfer of a coenzyme A group from an acyl-CoA donor to a carboxylic acid acceptor. Among other roles, they are responsible for transfer of CoA groups during fermentation and metabolism of ketone bodies. These enzymes are found in all three domains of life.
