The citric acid cycle (CAC) – also known as the TCA cycle or the Krebs cycle – is a series of chemical reactions to release stored energy through the oxidation of acetyl-CoA derived from carbohydrates, fats, and proteins. The TCA cycle is used by organisms that respire 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 and may have originated abiogenically. 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.
Lysine (symbol Lys or K) is an α-amino acid that is used in the biosynthesis of proteins. It contains an α-amino group (which is in the protonated −NH3+ form under biological conditions), an α-carboxylic acid group (which is in the deprotonated −COO− form under biological conditions), and a side chain lysyl ((CH2)4NH2), classifying it as a basic, charged (at physiological pH), aliphatic amino acid. It is encoded by the codons AAA and AAG. Like almost all other amino acids, the α-carbon is chiral and lysine may refer to either enantiomer or a racemic mixture of both. For the purpose of this article, lysine will refer to the biologically active enantiomer L-lysine, where the α-carbon is in the S configuration.
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.
2-hydroxyglutaric aciduria is a rare neurometabolic disorder characterized by the significantly elevated levels of hydroxyglutaric acid in one's urine. It is either autosomal recessive or autosomal dominant.
In enzymology, a homoserine dehydrogenase (EC 1.1.1.3) is an enzyme that catalyzes the chemical reaction
In enzymology, a homoisocitrate dehydrogenase (EC 1.1.1.87) is an enzyme that catalyzes the chemical reaction
In enzymology, a 4-phosphoerythronate dehydogenase (EC 1.1.1.290) is an enzyme that catalyzes the chemical reaction
In enzymology, a 3alpha(or 20beta)-hydroxysteroid dehydrogenase (EC 1.1.1.53) 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, an L-2-hydroxyglutarate dehydrogenase is an enzyme that catalyzes the chemical reaction
In enzymology, a D-lactate dehydrogenase (cytochrome) is an enzyme that catalyzes the chemical reaction
In enzymology, a hydroxyacid-oxoacid transhydrogenase is an enzyme that catalyzes the chemical reaction
In enzymology, a saccharopine dehydrogenase (NAD+, L-lysine-forming) (EC 1.5.1.7) is an enzyme that catalyzes the chemical reaction
In enzymology, a 2-hydroxyglutarate synthase (EC 2.3.3.11) is an enzyme that catalyzes the chemical reaction
Posphoglycerate dehydrogenase {PHGDH} is an enzyme that catalyzes the chemical reactions
D-2-hydroxyglutarate dehydrogenase, mitochondrial is an enzyme that in humans is encoded by the D2HGDH gene.
L-2-hydroxyglutarate dehydrogenase, mitochondrial is an enzyme that in humans is encoded by the L2HGDH gene, also known as C14orf160, on chromosome 14.
Alpha-aminoadipic semialdehyde synthase is an enzyme encoded by the AASS gene in humans and is involved in their major lysine degradation pathway. It is similar to the separate enzymes coded for by the LYS1 and LYS9 genes in yeast, and related to, although not similar in structure, the bifunctional enzyme found in plants. In humans, mutations in the AASS gene, and the corresponding alpha-aminoadipic semialdehyde synthase enzyme are associated with familial hyperlysinemia. This condition is inherited in an autosomal recessive pattern and is not considered a particularly negative condition, thus making it a rare disease.
α-Hydroxyglutaric acid is an alpha hydroxy acid form of glutaric acid.
