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. Author manuscript; available in PMC: 2014 Sep 17.
Published in final edited form as: Biochemistry. 2013 Sep 5;52(37):10.1021/bi400965u. doi: 10.1021/bi400965u

FIGURE 6.

FIGURE 6

Proposed schemes for the reactions among the wild-type and axial mutant proteins of holoShp and apoHtsA. M66/M153 and M79/H229 are the axial ligand residues in Shp and HtsA, respectively, and are also represented by X and Y when their identity and relative locations cannot be specified. The short lines to heme represent the axial bonds to the heme iron. A, the model for the Shp-to-HtsA heme transfer in which the Met66 and M153 axial residues of holoShp are specifically displaced by the Met79 and His229 residues of apoHtsA, respectively. B, reaction scheme for the kinetically biphasic ferric holoShp/apoHtsAM79A reaction. C & D, kinetically single-phase (c) and biphasic (D) reactions of ferric holoShp axial mutants with apoHtsA axial mutants.