Localization of the enzymes involved in H2 and formate metabolism in Syntrophospora bryantii.

Cell-free extracts of crotonate-grown cells of the syntrophic butyrate-oxidizing bacterium Syntrophospora bryantii contained high hydrogenase activities (8.5-75.8 mumol.min-1mg-1 protein) and relatively low formate dehydrogenase activities (0.04-0.07 mumol.min-1 mg-1 protein). The KM value and threshold value of the hydrogenase for H2 were 0.21 mM and 18 microM, respectively, whereas the KM value and threshold value of the formate dehydrogenase for formate were 0.22 mM and 10 microM, respectively. Hydrogenase, butyryl-CoA dehydrogenase and 3-OH-butyryl-CoA dehydrogenase were detected in the cytoplasmic fraction. Formate dehydrogenase and CO2 reductase were membrane-bound, likely located at the outer aspect of the cytoplasmic membrane. Results suggest that during syntrophic butyrate oxidation H2 is formed intracellularly while formate is formed at the outside of the cell.