Final answer:
The Carnitine Acylcarnitine Translocase (CACT) and Carnitine Acyltransferase I (CAT-I) are the active transporters within the carnitine shuttle during a fasted state. They help transport fatty acids into the mitochondria for energy production through fatty acid oxidation.
Step-by-step explanation:
The transporters within the carnitine shuttle that are active in a fasted state are the Carnitine Acylcarnitine Translocase (CACT) and Carnitine Acyltransferase I (CAT-I), also known as Carnitine Palmitoyltransferase I (CPT I). During fasting, when the body is in need of energy, it turns to fatty acids for fuel. These fatty acids are activated to fatty acyl-CoA in the cytoplasm, but they cannot directly cross the mitochondrial membranes due to their impermeable nature. This is where the carnitine shuttle comes into play.
Fatty acyl-CoA is first converted to acyl-carnitine by CAT-I, which is found on the outer mitochondrial membrane. The acyl-carnitine is then transported across the inner mitochondrial membrane by CACT. Once inside the mitochondria, Carnitine Acyltransferase II (CAT-II) converts acyl-carnitine back into acyl-CoA, allowing for subsequent fatty acid oxidation in the mitochondrial matrix. The free carnitine, which is left behind, is shuttled back out into the cytosol to continue the cycle, making this process a crucial part of energy metabolism, especially during periods where glucose supply is low.