A chemical interpretation of the mechanism of oxidation by dehydrogenase enzymes

Abstract

General analogies between biochemical oxidations catalyzed by dehydrogenases and free-radical chain oxidations were pointed out and special emphasis was given to the fact that free radicals regularly dehydrogenate aliphatic molecules. An enzyme catalyst was regarded as a supplier of an active free radical, whereby a chain reaction involving a substrate and a coenzyme, and ultimately oxygen or an oxidizing agent, was set up. This scheme was applied to several dehydrogenase systems and the special role of phosphates in enzyme reactions was discussed. It was pointed out that many known enzymes gave either free radicals by dissociation of prosthetic groups (e.g., flavoproteins), or else initiated single electron oxidations and reductions (e.g., Fe-porphyrins). The inhibition of specific enzymes by substances such as KCN or Na iodoacetate was explained as a destruction of free radicals, or as a replacement of active radicals by others too inert to perpetuate the reaction chain.