Reactivity of nicotinamide-adenine dinucleotide dimer in plant phenol oxidase systems

• Published in: Archives of biochemistry and biophysics Vol. 159; no. 2; pp. 837 - 841
• Main Authors: Fricks, Dot H., Bechtel, Jack T., Underwood, A.L.
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 01.01.1973
• Subjects: mung beans
• ISSN: 0003-9861; 1096-0384
• DOI: 10.1016/0003-9861(73)90525-0

The enzymie system in mung bean seedlings which earlier workers characterized as a diaphorase capable of oxidizing the 1,2- and 1,6-dihydropyridine isomers of NADH is, in fact, a phenol oxidase. The NAD species whose oxidation was observed is actually the dimeric 1-electron product obtained in the electrolytic reduction of NAD + solutions. The unidentified “cofactor” required along with the enzyme for the oxidation of the dimer is probably a naturally occurring phenol. Similar activity is found in a variety of plants, including other types of beans as well as corn, cotton, and wheat. The dimer is also reactive with respect to a commercial mushroom phenol oxidase preparation. It cannot be stated whether the NAD dimer is in any sense a natural reactant in such systems, but the supposedly unusual mung bean activity is clarified.