title: Synthesis and photophysical properties of zinc myoglobin appending an ethidium ion as a DNA intercalator.
abstract: In order to elucidate the intramolecular photoinduced electron-transfer or energy-transfer mechanisms of the zinc myoglobin (ZnMb) dyad and to construct a photoreaction system within a Mb-DNA complex, we newly prepared ZnMb appending an ethidium ion (Et(+)). The steady-state fluorescence of ZnMb-Et(+) at 600 nm and its lifetime (2.2 ns) indicate that the excited singlet state of (1)(ZnMb)* is not quenched by the Et(+) moiety, whereas the lifetime of the excited triplet state of (3)(ZnMb)*-Et(+) was shorter (tau = 4.3 ms) than those of ZnMb and the intermolecular (ZnMb + ethidium) system. Upon photoirradiation of Et(+), fluorescence studies indicated the intramolecular quenching reactions from the excited singlet state, (1)(Et(+))*, to ZnMb, the process of which is likely the photoinduced energy-transfer reaction via a through-space mechanism. We also demonstrate the photophysical and spectroscopic properties of ZnMb-Et(+) in the presence of calf thymus (CT) DNA. The changes in the absorption and fluorescence spectra of ZnMb-Et(+) on the addition of CT-DNA up to 15 equiv were very small, indicating that there are no major changes in the heme pocket. However, we observed a longer lifetime of (3)(ZnMb)*-Et(+) in the presence of CT-DNA (tau = 5.3 ms) by single flash photolysis. This was induced by noncovalent interactions between Et(+) and CT-DNA, followed by a conformational change of Et(+) at the surface of ZnMb, where the donor-acceptor distance was probably elongated by CT-DNA. The synthetic manipulation at the Mb surface, by using a DNA intercalator coupled with photoinduced reaction, may provide a sensitive transient signal for DNA and valuable information to construct new Mb-DNA complex.
authors.affiliation: Department of Chemistry, Nara Women's University, Nara, 630-8506, Japan. hiroshi@cc.nara-wu.ac.jp
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Takashima
authors.forename: Yukiko
authors.initials: Y
authors.lastname: Matsushima
authors.forename: Yasuyuki
authors.initials: Y
authors.lastname: Araki
authors.forename: Osamu
authors.initials: O
authors.lastname: Ito
authors.forename: Keiichi
authors.initials: K
authors.lastname: Tsukahara
mesh_terms: D000042:Absorption; D000818:Animals; D002417:Cattle; D004247:DNA / Q000737:chemistry*; D004579:Electron Transport; D004735:Energy Transfer; D004996:Ethidium / Q000737:chemistry*; D005453:Fluorescence; D007364:Intercalating Agents / Q000138:chemical synthesis* / Q000737:chemistry; D007700:Kinetics; D009211:Myoglobin / Q000737:chemistry*; D011524:Protoporphyrins / Q000737:chemistry; D013056:Spectrophotometry, Ultraviolet; D015032:Zinc / Q000737:chemistry*
chemical_list: D007364:Intercalating Agents; D009211:Myoglobin; D011524:Protoporphyrins; C017803:zinc protoporphyrin; D004247:DNA; C427203:calf thymus DNA; D004996:Ethidium; D015032:Zinc