Purification and properties of the aldehyde oxidases from hog and rabbit livers.

The aldehyde oxidases from rabbit and hog livers have been purified to homogeneity by modifications of and additions to previously published procedures. The final preparations were judged to be homogeneous on the basis of ultracentrifugal, electrophoretic, chromatographic, spectral, and kinetic criteria. A number of physical and kinetic properties of the homogeneous enzymes have been determined. The homogeneous enzymes have been shown to catalyze the oxidation of N’-methylnicotinamide to both N1-methyl-2-pyridone-S-carboxamide and N1-methyl-4-pyridone-3-carboxamide in a ratio (2-pyridone to the 4-pyridone) of 100 for the rabbit enzyme and 3.8 for the hog enzyme. The ratios of products formed by these enzymes at each step in their purifications were constant. The ratios of the pyridone products obtained on the oxidation of several N’substituted analogues of Nl-methylnicotinamide by these aldehyde oxidases have been found to shift in favor of the 4-pyridone as the bulk of the N-substituent was increased. A general mechanism of action of aldehyde oxidases is proposed which accounts for the different pyridone ratios and the unique kinetic properties associated with the different forms of the enzyme which have been found in a number of different mammalian livers.