Functional analysis of the iron(II) etiocorrphycene incorporated in the myoglobin heme pocket

The iron(III) complex of 2,7,12,17-tetraethyl-3,6,11,18-tetra-methylcorrphycene, an isomeric heme, was complexed with apomyoglobin to examine the ligand binding ability of the novel macrocycle under physiological conditions. The reconstituted holoprotein was found to be functionally active at pH 7.4 and 20 degrees C and to bind oxygen and carbon monoxide reversibly with a half-saturation pressure at 6.7 and 3.5mmHg, respectively. Equilibrium affinities for these ligands are one to two orders of magnitude lower than those reported for native myoglobin. The functional anomaly was ascribed to the geometric and electronic strain on the iron(II) atom in the trapezoidal coordination core of corrphycene.