Nicotinic acid metabolism. IV. Ferredoxin-dependent reduction of 6-hydroxynicotinic acid to 6-oxo-1,4,5,6-tetrahydronicotinic acid.

Previous reports from this laboratory have described the isolation of 6-hydroxynicotinic acid and 6-0x0-1 ,4,5,6-tetrahydronicotinic acid from the reaction media of a clostridial species grown on nicotinic acid (1). Bn enzyme that catalyzes the reversible oxidation of nicotinic acid to HNA’ has been purified from extracts of this microorganism (2). Since fortified crude extract of this Clostridium can metabolize HNA as well as nicotinic acid (l), this degradation was studied to define further the fermentation of nicotinic acid in this microorganism and the role of 6-0x0-1 ,4,5,6-tetrahydronicotinic acid. This paper reports the partial purification of an enzyme which catalyzes the reversible reduction of HNA to the 4-5-dihydroderivative, 6-0x0-1,4,5,6-tetrahydronicotinic acid. This enzyme requires reduced ferredoxin or reduced methyl viologen dye as the electron donor for the reduction of HNA.