Substrate Specificity of Formaldehyde Dehydrogenase fromPseudomonas putida

The substrate specificity of formaldehyde dehydrogenase purified from a cell-free extract of Pseudomonas putida C-83 was reinvestigated with a series of aldehyde and alcohol substrates. The activities toward formaldehyde and n-butanol were almost parallel throughout the procedures of enzyme purification and pH-stability experiments, suggesting that the same enzyme protein shows dehydrogenase activities for both aldehyde and alcohol substrates. Formaldehyde was the best substrate and the enzyme showed reduced activity with increasing length of alkyl groups of aldehydes, no activity being detected for n-butyraldehyde. Among the alcohol substrates, n-pentanol was the best substrate, and no activity was observed for methanol or ethanol. The enzyme activity for alcohols increased with increasing length of alkyl groups until n-pentanol and then decreased gradually. The dehydrogenase activity toward formaldehyde was inhibited competitively by other aldehydes but noncompetitively by n-butanol and n-hexanol. On the other hand, the type of inhibition by aldehydes for n-butanol dehydrogenation varied depending upon the length of alkyl groups of aldehydes used.