Abstract
Formaldehyde dehydrogenase (PFDH) was isolated from the creatinine-decomposing bacterium Pseudomonas putida, and its gene has been cloned. PFDH is unique because it was the only enzyme that catalyzed the dehydrogenation of formaldehyde without glutathione. PFDH belongs to a zinc-containing alcohol dehydrogenase family. Quantitative analysis of the reaction products using NMR revealed that the enzyme is not simply a dehydrogenase but is an aldehyde dismutase catalyzing a simultaneous conversion of both aldehyde to carboxylate and aldehyde to alcohol. The enzyme contains a tightly bound cofactor of NAD+/NADH per subunit and is classified as a nicotinoprotein. The enzyme reaction can proceed without external addition of the nucleotide cofactor. The formaldehyde was crystallized using the hanging-drop vapor diffusion method with ammonium sulfate as a precipitant. The crystal structure was determined using the multiwavelength anomalous diffraction method with intrinsic zinc ions. The overall structure of PFDH is similar to that of a classic horse liver alcohol dehydrogenase. However, a comparison of these structures indicated that the insertion loop specifically found in PFDH may be responsible for the tight binding of the cofactor, thereby making PFDH a dismutase.
