LOCALIZATION OF THE ENZYMES INVOLVED IN H-2 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 mu mol . min(-1)mg(-1) protein) and relatively low formate dehydrogenase nase activities (0.04-0.07 mu mol . min(-1)mg(-1) protein). The K-M value and threshold value of the hydrogenase for H-2 were 0.21 mM and 18 mu M, respectively, whereas the K-M value and threshold value of the formate dehydrogenase for formate were 0.22 mM and 10 mu M, 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 H-2 is formed intracellularly while formate is formed at the outside of the cell.