One-electron reactions in biochemical systems as studied by pulse radiolysis. I. Nicotinamide-adenine dinucleotide and related compounds

Abstract

1. Some univalent oxidations and reductions of NAD and related compounds have been studied by means of pulse radiolysis. 2. Both hydrated electrons and the COO − radical will reduce NAD + with rate constants of k = 2.5·10 10 M −1·sec −1 and 1.6·10 9 M −1·sec −1 respectively. 3. The reduction leads to a single free radical whose unpaired electron is located at the nicotinamide end of the molecule. By using AMP it has been shown that the addition of an electron to the adenine group is followed by efficient electron transfer to the nicotinamide group. 4. The absorption spectra of the free radicals formed from NAD and 1-methyl-nicotinamide chloride have been determined, and shown to resemble published absorption spectra of related free radicals. 5. The NAD (or 1-methylnicotinamide chloride) free radicals have been shown to react with each other with a rate constant of k = 5.6·10 7 M −1·sec −1 ( k = 6.9·10 7 M −1·sec −1 for 1-methylnicotinamide chloride), probably to give a dimer, as in previous experiments using X-irradiation.