Green, J. H. (Michigan State University, East Lansing), and H. L. Sadoff. Comparison of soluble reduced nicotinamide adenine dinucleotide oxidases from cells and spores of Clostridium botulinum. J. Bacteriol. 89:1499-1505. 1965.-The properties of purified reduced nicotinamide adenine dinucleotide (NADH(2)) oxidases from cells and spores of Clostridium botulinum 62-A have been studied to determine whether they are the same or different proteins. The spore NADH(2) oxidase was very heat-stable, whereas the vegetative enzyme was readily denatured at 70 C. The spore oxidase exhibited less affinity for the substrate than did the vegetative protein, but possessed a tightly bound cofactor. Atabrine was a noncompetitive inhibitor for both enzymes, but was less inhibitory to the spore NADH(2) oxidase. The enzymes could be separated from each other by gel filtration or chromatography on a diethylaminoethyl-cellulose column. The molecular weight of the spore oxidase was estimated to be 200,000 or greater, whereas that of the vegetative enzyme was 100,000 or less. Neither NADH(2) oxidase would cross-react with its heterologous antibody in a precipitation reaction. The conclusion drawn from this investigation is that the two NADH(2) oxidases are distinctly different proteins.