The porcine liver general acyl CoA dehydrogenase catalyzes the oxidation of saturated acyl CoA thiolesters to the trans-2, 3-enoyl CoA product. The kinetic and substrate binding properties of the enzyme has been studied by steady state and transient kinetic techniques; and equilibrium binding methods using dead end inhibitors. We propose to further study the catalytic mechanism of the dehydrogenase using 2,3 deuterated acyl CoA substrates. Previous experiments suggest negative cooperativity in the enzyme. Results obtained from transient kinetic studies with deuterated substrates as well as proposed analyses of the subunit structure of the enzyme should clarify the aspect of cooperativity in the dehydrogenase. Since most fatty acids presented to liver are long chain fatty acids we are accumulating long chain acyl CoA dehydrogenase. Theoretically regulation of fatty acid oxidation would occur at the level of the long chain dehydrogenase. Studies on regulation of this dehydrogenase will be undertaken as soon as sufficient long chain dehydrogenase is accumulated.