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Characterization of Catalytic Activities and Heme Coordination Structures of Heme–DNA Complexes Composed of Some Chemically Modified Hemes and an All Parallel-Stranded Tetrameric G-Quadruplex DNA Formed from d(TTAGGG)

Shinomiya, Ryosuke, Katahira, Yuya, Araki, Haruka, Shibata, Tomokazu, Momotake, Atsuya, Yanagisawa, Sachiko, Ogura, Takashi, Suzuki, Akihiro, Neya, Saburo, Yamamoto, Yasuhiko
Biochemistry 2018 v.57 no.41 pp. 5930-5937
carbon monoxide, catalytic activity, chemical bonding, enzyme activity, heme, histidine, iron, ligands, myoglobin, peroxidase, reaction mechanisms
Heme binds selectively to the 3′-terminal G-quartet (G6 G-quartet) of an all parallel-stranded tetrameric G-quadruplex DNA, [d(TTAGGG)]₄, to form a heme–DNA complex. Complexes between [d(TTAGGG)]₄ and a series of chemically modified hemes possessing a heme Fe atom with a variety of electron densities were characterized in terms of their peroxidase activities to evaluate the effect of a change in the electron density of the heme Fe atom (ρFₑ) on their activities. The peroxidase activity of a complex decreased with a decreasing ρFₑ, supporting the idea that the activity of the complex is elicited through a reaction mechanism similar to that of a peroxidase. In the ferrous heme–DNA complex, carbon monoxide (CO) can bind to the heme Fe atom on the side of the heme opposite the G6 G-quartet, and a water molecule (H₂O) is coordinated to the Fe atom as another axial ligand, trans to the CO. The stretching frequencies of Fe-bound CO (νCO) and the Fe–C bond (νFₑ–C) of CO adducts of the heme–DNA complexes were determined to investigate the structural and electronic natures of the axial ligands coordinated to the heme Fe atom. Comparison of the νCO and νFₑ–C values of the heme–DNA complexes with those of myoglobin (Mb) revealed that the donor strength of the axial ligation trans to the CO in a complex is considerably weaker than that of the proximal histidine in Mb, as expected from the coordination of H₂O trans to the CO in the complex.