Description:
<jats:title>Abstract</jats:title><jats:p>The biological function of the core modified porphyrin isomers such as porphycene, corrphycene, and hemiporphycene was examined. The iron complexes stoichiometrically coupled with apomyoglobin to afford stable holoproteins. The oxygen affinity of the reconstituted myoglobins (Mbs) changed over a 60 000‐fold range depending on the molecular structure of the prosthetic groups. For instance, a corrphycene with electronegative substituents to the bipyrrole part reduced the oxygen affinity of Mb to <jats:italic>P</jats:italic><jats:sub>50</jats:sub> = 300 mm Hg while the porphycene‐substituted Mb exhibited a <jats:italic>P</jats:italic><jats:sub>50</jats:sub> = 0.005 mm Hg. A notable increase in the oxygen delivery capacity of the corrphycene‐substituted Mb was explained on the basis of the trapezoidal corrphycene shape that stabilizes the iron displacement from the macrocycle plane toward the proximal histidine. The above observations demonstrate that the core modified heme isomers serve as novel molecular tools to regulate the oxygen affinity of Mb.</jats:p>