Dye-linked dehydrogenase activities for formate and formate esters in Amycolatopsis methanolica : characterization of a molybdoprotein enzyme active with formate esters and aldehydes

Cell-free extracts of methanol-grown Amycolatopsis methanolica contain dye-linked dehydrogenase activities for formate and methyl formate. Fractionation of the extracts revealed that the (unstable) activity for formate resides in membrane particles, while that for methyl formate belongs to a soluble enzyme that was purified and characterized. The enzyme, indicated as formate-ester dehydrogenase, appeared to be a molybdoprotein (4 Fe, 3 or 4 S, 1 Mo and 1 FAD were found for each enzyme molecule), with a molecular mass of 186 kDa and consisting of two subunits of equal size. Product identification suggests that the formate moiety in the ester becomes hydroxylated to a carbonate group after which the unstable alkyl carbonate decomposes into CO2 and the alcohol moiety. Based on structural and catalytic characteristics, the enzyme appears to be very similar to an enzyme isolated from Comamonas testosteroni [Poels, P. A., Groen, B. W. & Duine, J. A. (1987) Eur. J. Biochem. 166, 575-579] which was at that time considered to be an aldehyde dehydrogenase. Formate-ester dehydrogenase activity appeared to be present in several other bacteria. Possible roles for the A. methanolica enzyme in C1 dissimilation (oxidation of methyl formate to methanol and CO2 or a factor-formate adduct to factor plus CO2) or in general aldehyde oxidation, are discussed.