American Chemical Society
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Photophysical and DNA-Binding Properties of Cytochrome c Modified with a Platinum(II) Complex

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journal contribution
posted on 2010-11-04, 00:00 authored by Hiroshi Takashima, Miho Kitano, Chiharu Hirai, Hiroshi Murakami, Keiichi Tsukahara
Cytochrome c (cyt c) derivatives modified with a platinum(II) complex at the lysine residue, cyt c(III)-[Pt(bpy)(dapap)]1 {bpy = 2,2′-bipyridine, and dapap = 3-(2,3-diaminopropionylamino)propionic acid}, have been prepared. The modified residues are Lys8, Lys13, Lys55, Lys60, Lys73, and Lys88. In the case of the cyt c(III)-[Pt(bpy)(dapap)]1 dyad, the photoexcited singlet state of 1([Pt(bpy)(dapap)]1)* was quenched by the heme Fe(III) moiety through the intramolecular photoinduced energy-transfer reaction via a through-space mechanism. Next, in the presence of calf thymus (CT)-DNA, the DNA-responsive fluorescence properties of cyt c(III)-[Pt(bpy)(dapap)]1 isomers were investigated. The order of the obtained binding constants between the cyt c(III)-[Pt(bpy)(dapap)]1 isomer and CT-DNA in an aqueous solution suggested that the electrostatic interaction is one of the important factors to stabilize the cyt c-DNA complex. Finally, we discussed the rotational motion of the [Pt(bpy)(dapap)]2+ moiety at the surface of cyt c by fluorescence anisotropy measurement. The increase in the anisotropy parameter, r, for each cyt c isomer clearly revealed that the noncovalent recognition of the [Pt(bpy)(dapap)]2+ moiety by CT-DNA is an essential event in the formation of the cyt c-DNA complex and generation of DNA-sensitive fluorescence signals.