Yeast damage associated response protein (Dap1p) and mouse progesterone receptor membrane component-1 protein (mPGRMC1p) belong to a highly conserved class of putative membrane-associated progesterone binding proteins (MAPR), with Dap1p and inner zone antigen (IZA), the rat homologue of mPGRMC1p, recently being reported to bind heme. While primary structure analysis reveals similarities to the cytochrome b5 motif, neither of the two axial histidines responsible for ligation to the heme are present in any of the MAPR proteins. In the current paper, EPR, MCD, CD, UV-vis and general biochemical methods have been used to characterize the nature of heme binding in both Dap1p and a His-tagged, membrane anchor-truncated mPGRMC1p. As isolated, Dap1p is a tetramer which can be converted to a dimer upon addition of 150 mM salt. The heme is non-covalently attached, with a maximal, in vitro, heme loading of approximately 30%, for both proteins. CD and fluorescence spectroscopies indicate a well ordered structure, suggesting the low heme loading is probably not due to improperly folded protein. EPR confirmed a five coordinate, high-spin, ferric resting state for both proteins, indicating one axial amino acid ligand, in contrast to the six coordinate, low-spin, ferric state of cytochrome b5. The MCD spectrum confirmed this conclusion for Dap1p and indicated the axial ligand is most likely a tyrosine and not a histidine, nor a cysteine, however an aspartic acid residue could not be conclusively ruled out. Potential axial ligands, which are conserved in all MAPR’s, were mutated (Y78F, D118A and Y138F) and purified to homogeneity. The mutants Y78F and D118A were found to bind heme, however, Y138F did not. This result is consistent with the MCD data and indicates that Tyr138 is most likely the axial ligand to the heme in Dap1p.