In the mitochondrial ß-oxidation cycle, the conversion of straight-chain acyl-CoAs into 2-trans-enoyl-CoAs is catalyzed by acyl-CoA dehydrogenases, differing in chain length specificities. Phenylpropionyl-CoA is specificly accepted by Medium-Chain Acyl-CoA Dehydrogenase yielding cinnamoyl-CoA as product. In a variety of cell types MCAD can be assayed spectrophotometrically by measuring at 308 nm the formation of cinnamoyl-CoA from phenylpropionyl-CoA in the presence of an artificial electron acceptor.
Yao K-W, Schulz H. Specific assay of Medium-Chain Acyl-CoA Dehydrogenase based on the spectrophotometric maesurement of product formation. Anal Biochem 214 (1993) 528-534.