Acyl-CoA dehydrogenases constitute a family of flavopro-teins that catalyze the a,b-dehydrogenation of fatty acid acyl-CoA conjugates. While they differ widely in their spe-cificity, they share the same basic chemical mechanism ofa,b-dehydrogenation. Medium chain acyl-CoAdehydro-genase is probably the best-studiedmember of the class and serves as a model for the study of catalytic mechanisms.