4.C.2 The Carnitine O-Acyl Transferase (CarAT) Family

Peroxisomes metabolize a variety of lipids, acting as a chain-shortening system that produces acyl-CoAs of varying chain lengths, including acetyl-CoA and propionyl-CoA. Peroxisomes contain carnitine acetyltransferase (CRAT) and carnitine octanoyltransferase (CROT) that produce carnitine esters for transport out of peroxisomes, together with recently characterized acyl-CoA thioesterases (ACOTs) that produce free fatty acids. Westin et al. (2008) performed tissue expression profiling of the short- and medium-chain carnitine acyltransferases Crat, Crot and the short- and medium-chain thioesterases (Acot12) and (Acot5). They provided evidence that these enzymes are largely expressed in different tissues and do not compete for the same substrates. Rather, they provide complementary systems for transport of metabolites across the peroxisomal membrane. This may explain earlier observed tissue differences in peroxisomal production of acetyl-CoA/acetyl-carnitine/acetate and underscores the differences in peroxisome function in various organs.

The group translocation reaction believed to be catalyzed by some CrAT family members is:

Acetyl-CoA + Carnitine CoA + O-Acetylcarnitine



Adeva-Andany, M.M., I. Calvo-Castro, C. Fernández-Fernández, C. Donapetry-García, and A.M. Pedre-Piñeiro. (2017). Significance of l-carnitine for human health. IUBMB Life. [Epub: Ahead of Print]

Westin, M.A., M.C. Hunt, and S.E. Alexson. (2008). Short- and medium-chain carnitine acyltransferases and acyl-CoA thioesterases in mouse provide complementary systems for transport of β- oxidation products out of peroxisomes. Cell. Mol. Life Sci. 65: 982-990.


TC#NameOrganismal TypeExample
4.C.2.1.1Peroxisomal carnitine O-acetyl transferase (carnitine acylase (CAT or CrAT))AnimalsCrAT of Homo sapiens (P43155)
4.C.2.1.2Peroxisomal carnitine O-octanoyl transferase (CrOT)AnimalsCrOT of Homo sapiens (Q9UKG9)

Carnitine palmitoyltransferase-1 is a transmembrane protein located in and on the outer mitochondrial membrane where it catalyzes the conversion of acyl-coenzyme A esters to acyl-carnitine esters (Adeva-Andany et al. 2017).

Carnitine palmitoyltransferase-1 of Homo spaines