The interaction of two long-chain acyl-CoA analogs with pig kidney general acyl-CoA dehydrogenase (EC 1.3.99,3) was examined. The effect of S-heptadecyl-CoA and heptadecan-2-onyl-dethio-CoA on the flavo-protein was observed spectrophotometrically using the flavin as an active-site probe. The S-heptadecyl thioether analog bound strongly to the enzyme (Kd = 17 nM) and was a powerful competitive inhibitor (Ki less than 40 nM). In contrast to the thioether analog, the dethiocarba derivative, heptadecan-2-onyl-dethio-CoA, was a substrate inthe standard assay system being dehydrogenated at about 60% of the rate shown by palmitoyl-CoA. These results support the proposal that alpha-carbanion formation is an early event in the dehydrogenation of acyl-CoA substrates.
