A. Location of the Eη and Fα His side chains on the PAS2-W276L structure (see Fig. 7). The distance from the Fe atom to the Eη His NE2 atom is 2.5 Å, whereas the distance from the Fe atom to the Fα His NE2 atom is 10.5 Å.
B. Average heme content of PAS1 [38–157] and PAS2 [165–282] peptides with Eη and Fα His replacements, given as a percentage of WT PAS heme content, corrected for peptide concentration. Error bars represent standard deviations from two to three experiments. The heme content of PAS1-H101A is significantly different from the heme content of PAS1-H101A/H106A (P < 0.05).