Definitions

transacylase

Malonyl-CoA

Malonyl-CoA is a coenzyme A derivative.

Functions

It plays a key role in chain elongation in fatty acid biosynthesis and polyketide biosynthesis.

Fatty acid biosynthesis

In the former, it provides 2-carbon units to fatty acids and commits them to fatty acid chain synthesis.

Malonyl-CoA is formed by carboxylating acetyl-CoA using the enzyme acetyl-CoA carboxylase. One molecule of acetyl-CoA joins with a molecule of carbon dioxide, requiring energy rendered from ATP.

Malonyl-CoA is utilised in fatty acid biosynthesis by the enzyme malonyl coenzyme A:acyl carrier protein transacylase (MCAT). MCAT serves to transfer malonate from malonyl-CoA to the terminal thiol of holo-acyl carrier protein (ACP).

Polyketide biosynthesis

Controversy still exists as to whether MCAT is also involved in bacterial polyketide biosynthesis, however there is evidence that the acyl carrier protein from a variety of bacterial polyketide synthases is capable of self-malonylation in the presence of malonyl-CoA.

Regulation

Malonyl-CoA is a highly-regulated molecule in fatty acid synthesis; as such, it inhibits the rate-limiting step in beta-oxidation of fatty acids. Malonyl CoA inhibits coenzyme A from associating with carnitine, thereby preventing coenzyme A from entering the mitochondria where fatty acid oxidation and degradation occur.

See also

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