Pyridine coenzymes. VIII. Autoxidation of the reduced form catalyzed by 4-amino-2,6-diiodophenol

Abstract

The reduced pyridine coenzymes are stoichiometrically and directly oxidized by molecular oxygen to the pyridinium form, under the catalytical effect of protonated 4-amino-2,6-diiodophenol. With the model coenzyme, 1 -benzyl-1,4-dihydronicotinamide, two processes take place simultaneously: (i) the direct oxidation and (ii) addition to the 5,6-double bond of the dihydronicotinamide followed by autoxidation of the rein the precedent paper (Schreier and Cilento, 1969) it was reported that o-halogenophenols, including thyroid hormones, catalyze the hydration of 1,4dihydronicotinamides. We have now found that DIPAP1 not only catalyzes solvent addition to 1-benzyl-1,4-dihydronicotinamide, a model coenzyme, but also the autoxidation of the resulting or intermediate products as well as of the model itself. In the case of the natural coenzymes, NADH and NADPH, only the autoxidation occurs with stoichiometric formation of NAD, and, almost so, of NADP. This work joins and significantly expands another line of research, that of nonclassical oxygen activation Zinner, 1966, 1967a-c). The important novel feature is that DIPAP, unlike other nonclassical oxygen activators, does not catalyze the autoxidation of compounds which autoxidize by one electron or • atom transfer.