Fatty acid oxidation occurs in the mitochondrial matrix. However, long-chain fatty acyl-CoA molecules cannot cross the inner membrane to enter the matrix. The carnitine shuttle system transfers the acyl group from CoA to carnitine, which can enter the mitochondrial matrix.

Label the enzymes and compounds of the carnitine shuttle system. The following enzyme abbreviations are used: carnitine acyltransferase I, CAT1; mitochondrial carnitine acyltransferase II, CAT2; and carnitine/acylcarnitine translocase (carnitine carrier protein), CAT.

OH (CH3)3N-CH2-CH-CH-COO 1 cytosol O R-C-SCOA mitochondrial matrix OH (CH3)3N-CH2-CH-CH-COO 5 2 R-C-SCOA HSCOA HSCOA O R-C-O (CH3)3N-CH-CH-CH-COO 3 R-C-O (CH3)3N-CH-CH-CH-COO 7 CAT1 CAT acyl-carnitine carnitine CAT2