Exclusive hydrogen-dependent reduction of nitroblue tetrazolium by Hyd-1 and the Fdh-N/O enzymes. A: Total cell extracts (25 μg of protein) from the strains CPD17 (ΔhyaB hybC fdhE) and CP971 (ΔhycA-I) after anaerobic growth in TGYEP, pH 6.5 were applied to native-PAGE (7.5% w/v polyacrylamide) and the gels were subsequently stained for 3 h under a 100% hydrogen with PMS-NBT or BV-TTC as described in the Methods section. B: Cell extracts as in A from the strains MC4100, DHP-F2 (ΔhypF), FM460 (ΔselC), FTD22 (ΔhyaB), FTD67 (ΔhybC) and CP971 (ΔhycA-I) were submitted to native page (7.5% w/v polyacrylamide) and stained with PMS-NBT and formate under a 100% nitrogen atmosphere. The activities of the formate dehydrogenases N and O (Fdh-N/O) are given on the right hand side of the gel. Arrows indicate the top of the gel.