hydroxybutyrylCoA

Hydroxybutyryl-CoA refers to coenzyme A thioesters of hydroxybutyric acids, most commonly the 3-hydroxybutyryl-CoA isomer. It is a short-chain acyl-CoA that serves as an intermediate in various metabolic pathways, including fatty acid oxidation and the metabolism of polyhydroxyalkanoates in certain bacteria.

Chemically, hydroxybutyryl-CoA is a four-carbon acyl-CoA with a hydroxyl group on the beta carbon of the chain. The 3-hydroxy isomer exists in different stereoisomeric forms, and enzyme specificity can vary for these forms in different organisms. As a CoA thioester, it carries the high-energy thioester bond characteristic of fatty acid and polyketide metabolism.

In fatty acid beta-oxidation, hydroxybutyryl-CoA is an intermediate in the short-chain oxidation cycle. It is formed by hydration of crotonyl-CoA (trans-2-butenoyl-CoA) to 3-hydroxybutyryl-CoA, which can then be oxidized to 3-ketoacyl-CoA and subsequently cleaved to shorter acyl-CoA and acetyl-CoA units, contributing to cellular energy production.

Hydroxybutyryl-CoA also features in the biosynthesis and turnover of polyhydroxybutyrate (PHB) in bacteria. In PHB metabolism, 3-hydroxybutyryl-CoA serves as a monomer precursor for PHB synthesis via PHB synthase, and in PHB degradation it can be released as 3-hydroxybutyrate or re-enter central metabolism as CoA-linked intermediates.

Biological relevance spans prokaryotic and eukaryotic systems, with roles tied to energy metabolism and carbon storage polymer pathways.