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.
Biological carbon fixation or сarbon assimilation is the process by which inorganic carbon is converted to organic compounds by living organisms. The compounds are then used to store energy and as structure for other biomolecules. Carbon is primarily fixed through photosynthesis, but some organisms use a process called chemosynthesis in the absence of sunlight.
Nicotinamide adenine dinucleotide phosphate, abbreviated NADP+ or, in older notation, TPN (triphosphopyridine nucleotide), is a cofactor used in anabolic reactions, such as the Calvin cycle and lipid and nucleic acid syntheses, which require NADPH as a reducing agent ('hydrogen source'). NADPH is the reduced form of NADP+, the oxidized form. NADP+ is used by all forms of cellular life.
In biochemistry, flavin adenine dinucleotide (FAD) is a redox-active coenzyme associated with various proteins, which is involved with several enzymatic reactions in metabolism. A flavoprotein is a protein that contains a flavin group, which may be in the form of FAD or flavin mononucleotide (FMN). Many flavoproteins are known: components of the succinate dehydrogenase complex, α-ketoglutarate dehydrogenase, and a component of the pyruvate dehydrogenase complex.
In enzymology, aldose reductase is a cytosolic NADPH-dependent oxidoreductase that catalyzes the reduction of a variety of aldehydes and carbonyls, including monosaccharides. It is primarily known for catalyzing the reduction of glucose to sorbitol, the first step in polyol pathway of glucose metabolism.
In enzymology, an acyl-CoA dehydrogenase (NADP+) (EC 1.3.1.8) is an enzyme that catalyzes the chemical reaction
In enzymology, a glutamate-5-semialdehyde dehydrogenase (EC 1.2.1.41) 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 CoA-glutathione reductase (EC 1.8.1.10) is an enzyme that catalyzes the chemical reaction
3-hydroxypropionate dehydrogenase (NADP+) (EC 1.1.1.298) is an enzyme with systematic name 3-hydroxypropionate:NADP+ oxidoreductase. This enzyme catalyses the following chemical reaction
Malonyl CoA reductase (malonate semialdehyde-forming) (EC 1.2.1.75, NADP-dependent malonyl CoA reductase, malonyl CoA reductase (NADP)) is an enzyme with systematic name malonate semialdehyde:NADP+ oxidoreductase (malonate semialdehyde-forming). This enzyme catalyse the following chemical reaction
3,4-Dehydroadipyl-CoA semialdehyde dehydrogenase (NADP+) (EC 1.2.1.77, BoxD, 3,4-dehydroadipyl-CoA semialdehyde dehydrogenase) is an enzyme with systematic name 3,4-didehydroadipyl-CoA semialdehyde:NADP+ oxidoreductase. This enzyme catalyses the following chemical reaction
Succinate-semialdehyde dehydrogenase (NADP+) (EC 1.2.1.79, succinic semialdehyde dehydrogenase (NADP+), succinyl semialdehyde dehydrogenase (NADP+), succinate semialdehyde:NADP+ oxidoreductase, NADP-dependent succinate-semialdehyde dehydrogenase, GabD) is an enzyme with systematic name succinate-semialdehyde:NADP+ oxidoreductase. This enzyme catalyses the following chemical reaction
Acrylyl-CoA reductase (NADPH) (EC 1.3.1.84) is an enzyme with systematic name propanoyl-CoA:NADP+ oxidoreductase. This enzyme catalyses the following chemical reaction
Crotonyl-CoA reductase (EC 1.3.1.86, butyryl-CoA dehydrogenase, butyryl dehydrogenase, unsaturated acyl-CoA reductase, ethylene reductase, enoyl-coenzyme A reductase, unsaturated acyl coenzyme A reductase, butyryl coenzyme A dehydrogenase, short-chain acyl CoA dehydrogenase, short-chain acyl-coenzyme A dehydrogenase, 3-hydroxyacyl CoA reductase, butanoyl-CoA:(acceptor) 2,3-oxidoreductase, CCR) is an enzyme with systematic name butanoyl-CoA:NADP+ 2,3-oxidoreductase. This enzyme catalyses the following chemical reaction
3-oxo-5,6-dehydrosuberyl-CoA semialdehyde dehydrogenase (EC 1.17.1.7, paaZ (gene)) is an enzyme with systematic name 3-oxo-5,6-dehydrosuberyl-CoA semialdehyde:NADP+ oxidoreductase. This enzyme catalyses the following chemical reaction
3-hydroxypropionyl-CoA dehydratase (EC 4.2.1.116) is an enzyme with systematic name 3-hydroxypropionyl-CoA hydro-lyase. This enzyme catalyses the following chemical reaction
4-hydroxybutanoyl-CoA dehydratase (EC 4.2.1.120) is an enzyme with systematic name 4-hydroxybutanoyl-CoA hydro-lyase. This enzyme catalyses the following chemical reaction
3-Hydroxypropionyl-CoA synthase is an enzyme with systematic name hydroxypropionate:CoA ligase (AMP-forming). This enzyme catalyses the following chemical reaction
