is a coenzyme A
It plays a key role in chain elongation in fatty acid
biosynthesis and polyketide
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).
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.
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.