asetyyliCoAn

asetyyliCoAn, commonly known as acetyl-CoA, is a central metabolite in aerobic respiration and lipid metabolism. It is a thioester formed between a coenzyme A molecule and an acetyl group. The thioester bond is a high-energy linkage that makes acetyl-CoA a versatile donor of acetyl groups in biochemical reactions.

Biosynthesis and sources: Most acetyl-CoA is produced in the mitochondrion by the pyruvate dehydrogenase complex, which converts pyruvate, derived from glycolysis, into acetyl-CoA with NADH and CO2 as byproducts. It is also generated by beta-oxidation of fatty acids in mitochondria and, to a lesser extent, catabolism of ketogenic amino acids. Cytosolic acetyl-CoA primarily arises from the export of citrate from mitochondria and its cleavage by ATP citrate lyase, enabling fatty acid and cholesterol synthesis.

Functions: In the Krebs cycle, acetyl-CoA combines with oxaloacetate to form citrate, releasing CoA and producing energy via NADH and FADH2. It also supplies acetyl groups for fatty acid synthesis, cholesterol biosynthesis, and protein acetylation, including histone acetylation, which can influence gene expression. Acetyl-CoA thus links carbohydrate, lipid, and protein metabolism and acts as a key regulatory metabolite.

Localization and transport: Mitochondrial acetyl-CoA participates in energy production; cytosolic acetyl-CoA is used for biosynthesis. The citrate shuttle permits its export to the cytosol.

See also: pyruvate dehydrogenase complex, beta-oxidation, fatty acid synthesis, histone acetylation, coenzyme A.