The carnitine transport system (also the carnitine-acyltransferase system , carnitine shuttle ) is one of several mitochondrial transport systems that transfer acyl-CoA via acylation of carnitine in the cytoplasm, through mitochondrial membranes into the matrix (transmembrane transfer). The system includes several enzymes: carnitine acyltransferase (also carnitine palmitoyl transferase , abbr. CPT) and a carrier protein - carnitine acyl carnitine translocase (abbreviation CACT). These enzymes are membrane proteins .
Content
- 1 Structure and transport mechanism
- 2 Pathology
- 3 Notes
- 4 See also
Transfer structure and mechanism
Activated short and medium hydrocarbon chain fatty acids can easily penetrate the mitochondrial double membrane, but most fatty acids have a long chain that interferes with the penetration of these acids into the inside. For this transfer, mitochondria have a system that allows such fatty acids to be transported through membranes via a carnitine shuttle. Fatty acids in the form of acyl-CoA become transportable in the cytoplasm of cells only after interaction with carnitine . The reaction mechanism is the transfer of an acyl group (COR) from an acyl-CoA molecule to a substrate - carnitine. The reaction is catalyzed by the enzyme carnitine-palmitoyltransferase I (CPT1). The resulting acylcarnitine diffuses through the outer membrane into the intermembrane space of the mitochondria to the inner membrane. The inner membrane is not permeable to acylcarnitine and, therefore, it is transported by a carrier protein - carnitine-acylcarnitine translocase (CACT), which penetrates through the inner membrane of mitochondria (it is a transmembrane protein ). This enzyme carries out the transfer of acylcarnitine by facilitating diffusion into the matrix . Further, acylcarnitine, under the action of coenzyme A (CoA-SH) and the carnitine-palmitoyltransferase II (CPT2) enzyme (located on the inner side of the inner membrane), is split into carnitine and acyl-CoA, which undergo further β-oxidation . Using the same translocase, carnitine is transferred into the intermembrane space and freely diffuses into the cytoplasm, where it is again acylated. The equations for the reactions of transfer of acyl-CoA to the matrix via the carnitine shuttle are as follows:
R-CO ~ SCoA + carnitine ↔ carnitine-COR + CoA-SH
and
CoA-SH + Carnitine-COR ↔ R-CO ~ SCoA + Carnitine
The first equation characterizes the acylation of carnitine, the second - the inverse process with the formation of acyl-CoA.
Pathology
Pathologies of the carnitine transport system are associated with genetic defects of the components that make up its composition. The most common is a deficiency of carnitine-palmitoyltransferase I.
Notes
See also
- Beta oxidation
- Carnitine O-Palmitoyltransferase