karnitiinshuttle

Karnitiinshuttle, also known as the carnitine shuttle or fatty acid shuttle, is a biological transport system crucial for cellular energy metabolism. It facilitates the movement of long-chain fatty acids from the cytoplasm into the mitochondria. This process is essential because the enzymes responsible for beta-oxidation, the breakdown of fatty acids for energy, are located within the mitochondrial matrix. Long-chain fatty acids, due to their hydrophobic nature and the impermeability of the inner mitochondrial membrane to them, require a specific mechanism to cross this barrier.

The carnitine shuttle involves a series of enzymes and transporters. Carnitine palmitoyltransferase I (CPT1), located on the outer mitochondrial membrane, catalyzes the formation of an ester bond between the fatty acid and carnitine, forming acylcarnitine. Acylcarnitine is then transported across the inner mitochondrial membrane by the carnitine-acylcarnitine translocase (CACT) transporter. Once inside the mitochondrial matrix, carnitine palmitoyltransferase II (CPT2), located on the inner side of the inner mitochondrial membrane, cleaves the acylcarnitine, releasing the fatty acid for beta-oxidation and regenerating free carnitine, which can then be transported back out.

This shuttle system is highly regulated and plays a significant role in cellular energy homeostasis, particularly during periods of fasting or increased energy demand when fatty acid oxidation becomes a primary fuel source. Deficiencies or dysfunctions in the carnitine shuttle can lead to various metabolic disorders, impacting muscle function and overall energy production.