“…MCD spectroscopy has been shown in many reports, and by us in reports describing the heme binding environment of both the complete proteins IsdA, IsdB, IsdC, IsdE, and as well the isolated NEAT domains of IsdA, IsdB (domain 2), IsdH (domain 3), and IsdC to exhibit parameters sensitive to the hemebinding axial ligands, oxidation state, and spin state (16,20,23,(25)(26)(27)(28)(29). 4 Previous reports of the mass spectral data have shown that the heme-free native apo-protein can be readily distinguished from the heme-free denatured apo-protein and the native, heme-bound holo-proteins (16,27,28). Extending the power of these two tools, we now demonstrate, for the first time, direct evidence for an ordered, multiprotein, heme transfer system between the Gram-positive bacterial surface Isd proteins.…”