Synthesis and Spectroscopic Properties of Reconstituted Zinc-Myoglobin Appending a DNA-Binding Platinum(II) Complex

Hiroshi Takashima, Emi Fujimoto, Chiharu Hirai, and Keiichi Tsukahara

Chem. Biodiv., 5, 2101-2112 (2008).

Abstract

A reconstituted zinc-myoglobin (ZnMb) dyad, ZnMb-[Pt(bpy)(en)]²⁺, has been prepared by incorporating chemically-modified zinc-porphyrin, being capable of DNA-binding of the Pt complex, [Pt(bpy)(en)]²⁺, where bpy and en are 2,2'-bipyridine and ethylenediamine, respectively.  The stedy-state fluorescence of the cofactor, [Pt(bpy)(μ-enPP)Zn]Cl₂, in MeOH indicates that the excited singlet state of zinc-porphyrin was almost quenched, probably because of the strong hydrophobic and π-π stacking interactions between the [Pt(bpy)(μ-enPP)Zn]²⁺ ions.  In the reconstituted ZnMb-[Pt(bpy)(en)]²⁺, the quenching reaction of ¹(ZnMb)* with the [Pt(bpy)(en)]²⁺ moiety does not occur, indicating apoMb matrix is essential.  On the other hand, when the [Pt(bpy)(en)]²⁺ moiety was excited, the enhancement of the fluorescence from ZnMb unit was observed.  It is suggested that the energy-transfer from ¹([Pt(bpy)(en)]²⁺)* to ZnMb occurs.  The spectral changes of ZnMb-[Pt(bpy)(en)]²⁺ in the presence of calf-thymus DNA were also provided.  Soret band at 428 nm gradually decreased and isosbestic points at 321, 414, and 432 nm were observed with increasing the DNA concentration.  When the Pt(II) moiety was excited at 321 nm, the fluorescence signal around 600 nm similarly decreased.  The synthetic manipulation of ZnMb by using a DNA-binding platinum(II) complex demonstrates sensitive fluorescence signal for DNA and valuable information to study photoinduced electron-transfer within a Mb-DNA complex.