FIG. 4.

Steady-state kinetic analysis of soluble iron reduction. Rates of TM-mediated (A) and whole-cell-mediated (B) iron reduction are expressed as moles of iron reduced per mole of OmcA per second (simplifying to s⁻¹). TM fractions (0.1 mg/ml) or whole-cell suspensions (see Materials and Methods) were added to 1-ml reaction mixtures containing buffer or defined medium and the specified concentrations of chelated iron species. The reaction was initiated upon the addition of 100 μl of 100 mM formate or 100 μl of the cell suspension. At 0, 15, and 30 min, 100-μl aliquots were removed and analyzed for ferrous iron (nanomoles of Fe²⁺ formed per minute per milligram of TM). Panel A shows results from TM incubations, and panel B shows results from whole-cell incubations with EDTA-Fe³⁺ (▪), NTA-Fe³⁺ (▿), or citrate-Fe³⁺ (•). Note the difference in scale between panels A and B.