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 biochemistry, an oxidoreductase is an enzyme that catalyzes the transfer of electrons from one molecule, the reductant, also called the electron donor, to another, the oxidant, also called the electron acceptor. This group of enzymes usually utilizes NADP+ or NAD+ as cofactors. Transmembrane oxidoreductases create electron transport chains in bacteria, chloroplasts and mitochondria, including respiratory complexes I, II and III. Some others can associate with biological membranes as peripheral membrane proteins or be anchored to the membranes through a single transmembrane helix.
A tetrose is a monosaccharide with 4 carbon atoms. They have either an aldehyde functional group in position 1 (aldotetroses) or a ketone functional group in position 2 (ketotetroses).
Malate dehydrogenase (EC 1.1.1.37) (MDH) is an enzyme that reversibly catalyzes the oxidation of malate to oxaloacetate using the reduction of NAD+ to NADH. This reaction is part of many metabolic pathways, including the citric acid cycle. Other malate dehydrogenases, which have other EC numbers and catalyze other reactions oxidizing malate, have qualified names like malate dehydrogenase (NADP+).
sn-Glycerol 3-phosphate is the organic ion with the formula HOCH2CH(OH)CH2OPO32-. It is one of three stereoisomers of the ester of dibasic phosphoric acid (HOPO32-) and glycerol. It is a component of glycerophospholipids. From a historical reason, it is also known as L-glycerol 3-phosphate, D-glycerol 1-phosphate, L-α-glycerophosphoric acid.
Fatty aldehyde dehydrogenase is an aldehyde dehydrogenase enzyme that in human is encoded in the ALDH3A2 gene on chromosome 17. Aldehyde dehydrogenase enzymes function to remove toxic aldehydes that are generated by the metabolism of alcohol and by lipid peroxidation.
Glycerol-3-phosphate dehydrogenase (GPDH) is an enzyme that catalyzes the reversible redox conversion of dihydroxyacetone phosphate to sn-glycerol 3-phosphate.
In enzymology, a sorbitol-6-phosphate dehydrogenase (EC 1.1.1.140) is an enzyme that catalyzes the chemical reaction
In enzymology, an erythrose-4-phosphate dehydrogenase (EC 1.2.1.72) is an enzyme that catalyzes the chemical reaction
In enzymology, a D-arabinitol 2-dehydrogenase (EC 1.1.1.250) is an enzyme that catalyzes the chemical reaction
In enzymology, a D-arabinitol 4-dehydrogenase (EC 1.1.1.11) is an enzyme that catalyzes the chemical reaction
In enzymology, a glycerol-3-phosphate dehydrogenase (NAD+) (EC 1.1.1.8) is an enzyme that catalyzes the chemical reaction
In enzymology, a mannitol-1-phosphate 5-dehydrogenase (EC 1.1.1.17) is an enzyme that catalyzes the chemical reaction
In enzymology, a ribitol 2-dehydrogenase (EC 1.1.1.56) is an enzyme that catalyzes the chemical reaction
In enzymology, a ribitol-5-phosphate 2-dehydrogenase (EC 1.1.1.137) is an enzyme that catalyzes the chemical reaction
In enzymology, a glyceraldehyde-3-phosphate dehydrogenase (NAD(P)+) (EC 1.2.1.59) is an enzyme that catalyzes the chemical reaction
In enzymology, a glyceraldehyde-3-phosphate dehydrogenase (phosphorylating) (EC 1.2.1.12) is an enzyme that catalyzes the chemical reaction
Inosine-5′-monophosphate dehydrogenase (IMPDH) is a purine biosynthetic enzyme that catalyzes the nicotinamide adenine dinucleotide (NAD+)-dependent oxidation of inosine monophosphate (IMP) to xanthosine monophosphate (XMP), the first committed and rate-limiting step towards the de novo biosynthesis of guanine nucleotides from IMP. IMPDH is a regulator of the intracellular guanine nucleotide pool, and is therefore important for DNA and RNA synthesis, signal transduction, energy transfer, glycoprotein synthesis, as well as other process that are involved in cellular proliferation.
D-arabinitol dehydrogenase (NADP+) (EC 1.1.1.287, NADP+-dependent D-arabitol dehydrogenase, ARD1p, D-arabitol dehydrogenase 1) is an enzyme with systematic name D-arabinitol:NADP+ oxidoreductase. This enzyme catalyses the following chemical reaction
