L-carnitine CoA-transferase (CaiB)

L-carnitine CoA-transferase is a bacterial enzyme, notably present in *Escherichia coli* and other gammaproteobacteria, that catalyzes the reversible transfer of a CoA group from gamma-butyrobetainyl-CoA or crotonobetainyl-CoA to L-carnitine, resulting in the formation of L-carnitinyl-CoA and gamma-butyrobetaine[2][4][5][7][8][9]. This enzyme (also called CaiB) is encoded by the cai operon, and is important in microbial carnitine and fatty acid metabolism. The enzyme belongs to the family III CoA-transferases and plays a central role in utilizing L-carnitine by enabling bacteria to produce energy from carnitine substrates under certain conditions[5][8]. The CaiB enzyme has been structurally characterized (dimer of subunits, with a Rossmann fold domain)[7]; its catalytic mechanism involves a covalent intermediate with an aspartate residue, allowing transfer of the CoA group between substrates[5][7]. Important note: L-carnitine CoA-transferase (CaiB) should not be confused with carnitine acetyltransferase (CRAT) or mitochondrial carnitine palmitoyltransferase enzymes, which are important in human fatty acid metabolism and disease. L-carnitine CoA-transferase is primarily characterized in bacteria and does not have a direct therapeutic or disease role in humans[2][4][5][7][8].

Other names

CaiBcrotonobetainyl/gamma-butyrobetainyl-CoA:carnitine CoA-transferasecrotonobetainyl-CoA:L-carnitine CoA-transferasegamma-butyrobetainyl-CoA:L-carnitine CoA-transferase

Catalyzes reversible transfer of CoA from gamma-butyrobetainyl-CoA (or crotonobetainyl-CoA) to L-carnitine, generating L-carnitinyl-CoA and gamma-butyrobetaine