asetyyliCoA

Acetyl-CoA, or acetyl coenzyme A, is a central metabolic intermediate and a thioester formed from acetate and coenzyme A. In cells, acetyl-CoA serves as the main donor of acetyl groups in many biosynthetic reactions and as a key substrate in energy metabolism. Its production and utilization are compartmentalized between mitochondria and the cytosol; acetyl-CoA itself cannot cross the inner mitochondrial membrane.

Major sources of acetyl-CoA include the oxidative decarboxylation of pyruvate by the pyruvate dehydrogenase complex in mitochondria, beta-oxidation of fatty acids, and the catabolism of certain ketogenic amino acids. In many tissues, acetyl-CoA generated in mitochondria is exported as citrate to the cytosol, where ATP citrate lyase converts citrate back to acetyl-CoA and oxaloacetate.

In the citric acid cycle, acetyl-CoA condenses with oxaloacetate to form citrate, yielding energy-rich NADH and FADH2. In cytosolic pathways, acetyl-CoA is a precursor for fatty acid synthesis (via malonyl-CoA), cholesterol biosynthesis via the mevalonate pathway, and ketone body formation in the liver during fasting.

Acetyl-CoA also serves as a substrate for protein acetylation, including histone acetylation, linking metabolism to gene regulation. The pool of acetyl-CoA depends on cellular energy status and is regulated by enzymes such as acetyl-CoA synthetase, acetyl-CoA carboxylase, and ATP citrate lyase.

Biochemical relevance: acetyl-CoA is derived from pantothenic acid (vitamin B5) as part of the coenzyme A structure; it acts as a key metabolic hub connecting carbohydrate, lipid, and protein metabolism and influencing metabolic disorders and energy homeostasis.