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.
In chemistry, hydroxylation can refer to:
Isocitrate dehydrogenase (IDH) (EC 1.1.1.42) and (EC 1.1.1.41) is an enzyme that catalyzes the oxidative decarboxylation of isocitrate, producing alpha-ketoglutarate (α-ketoglutarate) and CO2. This is a two-step process, which involves oxidation of isocitrate (a secondary alcohol) to oxalosuccinate (a ketone), followed by the decarboxylation of the carboxyl group beta to the ketone, forming alpha-ketoglutarate. In humans, IDH exists in three isoforms: IDH3 catalyzes the third step of the citric acid cycle while converting NAD+ to NADH in the mitochondria. The isoforms IDH1 and IDH2 catalyze the same reaction outside the context of the citric acid cycle and use NADP+ as a cofactor instead of NAD+. They localize to the cytosol as well as the mitochondrion and peroxisome.
The oxoglutarate dehydrogenase complex (OGDC) or α-ketoglutarate dehydrogenase complex is an enzyme complex, most commonly known for its role in the citric acid cycle.
Glyoxylic acid or oxoacetic acid is an organic compound. Together with acetic acid, glycolic acid, and oxalic acid, glyoxylic acid is one of the C2 carboxylic acids. It is a colourless solid that occurs naturally and is useful industrially.
In enzymology, a peptide-aspartate beta-dioxygenase (EC 1.14.11.16), a member of the alpha-ketoglutarate-dependent hydroxylases superfamily, is an enzyme that catalyzes the chemical reaction
In enzymology, a phytanoyl-CoA dioxygenase (EC 1.14.11.18) is an enzyme that catalyzes the chemical reaction
In enzymology, a procollagen-proline 3-dioxygenase (EC 1.14.11.7) is an enzyme that catalyzes the chemical reaction
Procollagen-proline dioxygenase, commonly known as prolyl hydroxylase, is a member of the class of enzymes known as alpha-ketoglutarate-dependent hydroxylases. These enzymes catalyze the incorporation of oxygen into organic substrates through a mechanism that requires alpha-Ketoglutaric acid, Fe2+, and ascorbate. This particular enzyme catalyzes the formation of (2S, 4R)-4-hydroxyproline, a compound that represents the most prevalent post-translational modification in the human proteome.
In enzymology, a taurine dioxygenase (EC 1.14.11.17) is an enzyme that catalyzes the chemical reaction.
In enzymology, a thymine dioxygenase (EC 1.14.11.6) is an enzyme that catalyzes the chemical reaction
In enzymology, a trimethyllysine dioxygenase (TMLH; EC 1.14.11.8) is an enzyme that catalyzes the chemical reaction
In enzymology, a 2-oxoglutarate synthase (EC 1.2.7.3) is an enzyme that catalyzes the chemical reaction
The enzyme 4-hydroxy-2-oxoglutarate aldolase catalyzes the chemical reaction
The enzyme oxalomalate lyase catalyzes the chemical reaction
In enzymology, a homocitrate synthase (EC 2.3.3.14) is an enzyme that catalyzes the chemical reaction
In enzymology, 4-aminobutyrate transaminase, also called GABA transaminase or 4-aminobutyrate aminotransferase, or GABA-T, is an enzyme that catalyzes the chemical reaction:
In enzymology, a L-lysine 6-transaminase is an enzyme that catalyzes the chemical reaction
Clavaminate synthase (EC 1.14.11.21, clavaminate synthase 2, clavaminic acid synthase) is an enzyme with systematic name deoxyamidinoproclavaminate,2-oxoglutarate:oxygen oxidoreductase (3-hydroxylating). This enzyme catalyses the following chemical reaction
Alpha-ketoglutarate-dependent hydroxylases are a major class of non-heme iron proteins that catalyse a wide range of reactions. These reactions include hydroxylation reactions, demethylations, ring expansions, ring closures, and desaturations. Functionally, the αKG-dependent hydroxylases are comparable to cytochrome P450 enzymes. Both use O2 and reducing equivalents as cosubstrates and both generate water.
