Formate dehydrogenase from Pseudomonas oxalaticus.

Formate dehydrogenase (EC 1.2.1.2) from Pseudomonas oxalaticus has been isolated and characterized. The enzyme (molecular weight 315000) is a complex flavoprotein containing 2 FMN, 18--25 non-heme iron atoms and 15--20 acid-labile sulphides. In the last step of the purification, a sucrose gradient centrifugation, a second catalytically active species has been found apparently originating from a dissociation of the enzyme into two equal subunits. The enzyme is specific toward its natural substrate formate. It transfers electrons to NAD+, oxygen, ferricyanide, and a lot of nonphysiological acceptors (dyes). In addition electrons are transferred from NADH to these acceptors. The (reversible) removal of FMN requires a reduction step. Reincorporation has been followed by the reappearance of the reactivity against formate and by fluorescence titration. The deflavo enzyme also binds FAD and riboflavin. The resulting enzyme species show characteristic catalytic abilities. Activity against formate is peculiar to the FMN species.