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Density functional study of roles of porphyrin ring in electronic structures of heme



Heme is a prosthetic group that consists of an iron ion contained in the center of a porphyrin, and a widely distributed cofactor in biology. It serves electron transfer and enzyme catalysis. There are many types of heme, which have several heme side chains such as propionyl, vinyl, and hydroxyfarnesylethyl groups. The differences in heme side chains yield many important functions. In this study, we have investigated the roles of porphyrin ring: heme porphyrin ring distortion, heme peripheral substitution, and protonation of propionyl group of heme, by using density functional theory with the polarizable continuum model. The effects of porphyrin ring of heme were discussed from the viewpoint of the charge density difference in the redox reaction and the redox potential. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009