HEMOPROTEIN MODELS BASED ON A COVALENT HELIX-HEME-HELIX SANDWICH .1. DESIGN, SYNTHESIS, AND CHARACTERIZATION

In this paper we describe the design, synthesis, and spectroscopic cha racterization of a covalent helix - heme - helix sandwich named Fe-III mimochrome I. It contains deuterohemin bound through both propionyl g roups to two identical Nand C-terminal protected nonapeptides as alpha -helical scaffolds. Each peptide moiety bears a His residue in the cen tral position, which acts as axial ligand to the metal ion. The newly developed synthetic strategy is based on a combination of solution and solid-phase methodologies. It represents a powerful method for obtain ing a large variety of analogues containing two symmetric or unsymmetr ic peptide chains covalently bound to the deuteroporphyrin ring. UV/Vi sible spectroscopic characterization in buffered 2,2,2-trifluoroethano l/water solution groves low-spin bis(histidine) iron(III) coordination ; circular dichroism (CD) measurements show an oc: helical conformatio n for the peptide moieties. Thus, all the data are in agreement with t he designed hypothetical model regarding both the iron(III) coordinati on and the peptide chain structural organization.