02 ± 0.64 0.49 ± 0.19 7.5 μM iron chloride (FeCl3) 3.63 ± 0.73 2.49 ± 0.64 15.3 μM hemin 1.72 ± 0.92 0.25 ± 0.18 10 μM potassium ferrocyanide Tipifarnib (K4[Fe(CN)6]) (Fe2+) 1.34 ± 1.30 0.38 ± 0.33 10 μM potassium Fer-1 mouse ferricyanide (K3[Fe(CN)6]) (Fe3+) 1.80 ± 2.82 0.93 ± 0.85 10 μM ferric ammonium sulfate (Fe(NH4)(SO4)2) 3.33 ± 2.53 2.02 ± 2.11 50 μM iron citrate (C6H5FeO7) 2.20 ± 0.70 3.47 ± 1.17 300 μM 2,2′-dipyridyl < 0.01 < 0.01 300 μM 2,2'-dipyridyl and 200 μM FeCl3 0.04 ± 0.07 < 0.01 300 μM 2,2'-dipyridyl and 200 μM iron citrate 1.59 ± 1.16 0.04 ± 0.06 a Cells were cultivated in M9 minimal medium including 0.8% (w/v) glucose. Iron sources were added

at the given final concentrations. b The activities were determined for triplicate experiments. Extracts of a hypF mutant, IKK inhibitor which cannot synthesize active

hydrogenases [16], had essentially no hydrogenase enzyme activity and served as a negative control. Extracts of the feoB::Tn5 mutant PM06 grown in M9 medium in the absence of iron had a total hydrogenase activity that was 24% that of the wild type without addition of iron compounds (Table 1). Growth of PM06 in the presence of iron chloride or ferric ammonium sulfate restored hydrogenase activity to levels similar to wild type. The exception was potassium ferricyanide, which failed to restore hydrogenase enzyme activity to wild type levels; instead activity was approximately Edoxaban 50% of that measured in MC4100 grown without iron supplementation and only 50% of that measured after growth of the wild type with potassium ferricyanide (Table 1). In contrast,

growth of PM06 in the presence of ferrocyanide did not restore hydrogenase activity. Addition of hemin as a source of oxidized iron also failed to restore hydrogenase activity to PM06, presumably because hemin cannot be taken up by E. coli and the oxidized iron is also tightly bound to the porphyrin. Taken together, these results are consistent with the ferrous iron transport system being an important route of iron uptake for hydrogenase biosynthesis in the wild type. Addition of 2, 2′-dipyridyl to the growth medium resulted in total loss of hydrogenase activity of the wild type MC4100 and PM06 (Table 1). Supplementation of 200 μM iron chloride or iron citrate together with 300 μM dipyridyl showed that iron citrate restored 66% of the wild type activity while iron chloride failed to restore activity. None of these additions restored hydrogenase activity to PM06. The activities of Hyd-1 and Hyd-2 can be visualized after non-denaturing PAGE followed by specific activity staining [14]; Hyd-3 is labile and cannot be visualized under these conditions. This method allows a specific analysis of the effect of mutations or medium supplements on Hyd-1 and Hyd-2 activity and it should be noted that this method is only semi-quantitative.