An essential methionine in pig kidney general acyl-CoA dehydrogenase

The flavoprotein pig kidney general acyl-CoA dehydrogenase contains a single catalytically essential methionine residue/FAD which reacts with iodoacetate at pH 6.6. S-Carboxymethylation of this residue generates an inactive enzyme derivative which retains FAD and the tetrameric structure of the native protein. The derivative binds actanoyl-CoA and palmityol-CoA with concomitant perturbation of the flavin chromophore, but the characterisitic spectrum of the reduced enzyme-enoyl-CoA complex is not observed. In addition, octanyol-CoA strongly protects the native enzyme against alkylation with iodoacetate. These results suggest that the methionine residue is within the active center of acyl-CoA dehydrogenase. Carboxymethylation of this residue may disrupt the precise orientation of the substrate required to achieve transfer of reducing equivalents to the flavin. Pig kidney general acyl-CoA dehydrogenase does not contain exposed catalytically essential cysteine residues.