Redox state and activity of molybdopterin cytosine dinucleotide (MCD) of CO dehydrogenase from Hydrogenophaga pseudoflava

Abstract

The redox state of molybdopterin cytosine dinucleotide (MCD) from the molybdo-iron-sulfur-flavoprotein CO dehydrogenase of the carboxidotrophic bacterium Hydrogenophaga pseudoflava has been studied. MCD has been purified as the dicarboxamidomethylated derivative (5,6-dihydro-di(cam)MCD) under conditions maintaining the native redox state. The full oxidation of di(cam)MCD released two electrons per molecule and revealed no intermediate. Apparently, MCD occurs in air-oxidized CO dehydrogenase in a redox state which is reduced by two electrons compared to the fully oxidized state. Due to the presence of 5'-cytidine monophosphate (5'-CMP) as a structural element, reduced di(cam)MCD (62 min half-life) was twice as stable towards air oxidation as reduced di(carboxamidomethyl)molybdopterin (di(cam)MPT) (36 min half-life).