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.
A dehydrogenase is an enzyme belonging to the group of oxidoreductases that oxidizes a substrate by reducing an electron acceptor, usually NAD+/NADP+ or a flavin coenzyme such as FAD or FMN. Like all catalysts, they catalyze reverse as well as forward reactions, and in some cases this has physiological significance: for example, alcohol dehydrogenase catalyzes the oxidation of ethanol to acetaldehyde in animals, but in yeast it catalyzes the production of ethanol from acetaldehyde.
In enzymology, a 4-hydroxybutyrate dehydrogenase (EC 1.1.1.61) is an enzyme that catalyzes the chemical reaction
In enzymology, a hydroxypyruvate reductase (EC 1.1.1.81) is an enzyme that catalyzes the chemical reaction
In enzymology, a 3-hydroxyacyl-CoA dehydrogenase (EC 1.1.1.35) is an enzyme that catalyzes the chemical reaction
In enzymology, a 3-hydroxypropionate dehydrogenase (EC 1.1.1.59) is an enzyme that catalyzes the chemical reaction
In enzymology, a 2,5-dioxovalerate dehydrogenase (EC 1.2.1.26) is an enzyme that catalyzes the chemical reaction
In enzymology, an aldehyde dehydrogenase (NAD+) (EC 1.2.1.3) is an enzyme that catalyzes the chemical reaction
In enzymology, an aldehyde dehydrogenase [NAD(P)+] (EC 1.2.1.5) is an enzyme that catalyzes the chemical reaction
In enzymology, an aminobutyraldehyde dehydrogenase (EC 1.2.1.19) is an enzyme that catalyzes the chemical reaction
In enzymology, an aminomuconate-semialdehyde dehydrogenase (EC 1.2.1.32) is an enzyme that catalyzes the chemical reaction
In enzymology, an aspartate-semialdehyde dehydrogenase is an enzyme that is very important in the biosynthesis of amino acids in prokaryotes, fungi, and some higher plants. It forms an early branch point in the metabolic pathway forming lysine, methionine, leucine and isoleucine from aspartate. This pathway also produces diaminopimelate which plays an essential role in bacterial cell wall formation. There is particular interest in ASADH as disabling this enzyme proves fatal to the organism giving rise to the possibility of a new class of antibiotics, fungicides, and herbicides aimed at inhibiting it.
In enzymology, a glutamate-5-semialdehyde dehydrogenase (EC 1.2.1.41) is an enzyme that catalyzes the chemical reaction
In enzymology, a L-aminoadipate-semialdehyde dehydrogenase (EC 1.2.1.31) is an enzyme that catalyzes the chemical reaction
In enzymology, a malonate-semialdehyde dehydrogenase (EC 1.2.1.15) is an enzyme that catalyzes the chemical reaction
In enzymology, a methylmalonate-semialdehyde dehydrogenase (acylating) (EC 1.2.1.27) is an enzyme that catalyzes the chemical reaction
In enzymology, a N-acetyl-gamma-glutamyl-phosphate reductase (EC 1.2.1.38) is an enzyme that catalyzes the chemical reaction
In enzymology, a succinate-semialdehyde dehydrogenase [NAD(P)+] (EC 1.2.1.16) is an enzyme that catalyzes the chemical reaction
Alanine dehydrogenase (EC 1.4.1.1) is an enzyme that catalyzes the chemical reaction
Methylmalonate-semialdehyde dehydrogenase [acylating], mitochondrial (MMSDH) is an enzyme that in humans is encoded by the ALDH6A1 gene.
