| Mechanistic aspects of two related enzymes, yeast acyl-CoA oxidase and pig kidney medium chain acyl-CoA dehydrogenase, have been investigated by chemical and spectroscopic approaches.;The acyl-CoA oxidase has been characterized by using a series of substrate analogues. Alkyl-SCoA thioethers from octyl-SCoA to hexadecyl-SCoA bind to the oxidase with progressively large spectral perturbation of the flavin chromophore and with an incremental binding energy of about 260 cal per methylene group. The binding between the oxidase and the analogues is fairly weak compared to the acyl-CoA dehydrogenase. Unstable long wavelength bands are observed when the enzyme reacts with some of the analogues, such as 3-thia- and 3-keto-acyl-CoA thioesters. These ligands are hydrolyzed by an unusual thioesterase activity of the oxidase releasing HSCoA and free fatty acids. The active site of the oxidase appears to be relatively open to solvent, an observation believed to be consistent with its high oxygen reactivity. In contrast, the acyl-CoA dehydrogenase reduced by substrate exhibits an extremely low reactivity toward molecular oxygen. The role of acyl-CoA thioester and its derivatives in the suppression of oxygen reactivity have been examined in detail. The photoreduced dehydrogenase is reoxidized by 120 ;A new class of acyl-CoA thioesters, 2-aza-acyl-CoA derivatives have been synthesized as additional tools in the study of the acyl-CoA dehydrogenase. They bind the medium chain acyl-CoA dehydrogenase rather tightly, for example, K... |
