FIG. 1.

Iron(III) reductase activity as a function of pH. The assay was done in a solution containing HEPES, MES (morpholineethane sulfonic acid), PIPES [piperazine-N,N′-bis(2-ethanesulfonic acid)], TAPS {N-[Tris-(hydroxymethyl)-methyl]-3-amino-propane sulfonic acid}, and KH₂PO₄ buffer, each constituent at a concentration of 20 mM. In addition, the reaction mixture contained 0.3 mM Fe(III)-NTA, 0.5 mM ferrozine, and 1 mM NADH.