title: Metal ion-dependent fluorescent dynamics of photoexcited zinc-porphyrin and zinc-myoglobin modified with ethylenediaminetetraacetic acid.
abstract: The reconstituted zinc-myoglobin (ZnMb) dyads, ZnMb-[M(II)(edta)], have been prepared by incorporating a zinc-porphyrin (ZnP) cofactor modified with ethylenediaminetetraacetic acid (H(4)edta) into apo-Mb. In case of the monomeric ZnP(edta) cofactor coordinated by one pyridine molecule, ZnP(py)(edta), a spontaneous 1:1 complex with a transient metal ion was formed in an aqueous solvent, and the photoexcited singlet state of ZnP, (1)(ZnP)*, was quenched by the [Cu(II)(edta)] moiety through intramolecular photoinduced electron-transfer (ET) reaction. The rate constant for the intramolecular quenching ET (k(q)) at 25 degrees C was successfully obtained as k(q) = 5.1 x 10(9) s(-1). In the case of Co(2+), Ni(2+), and Mn(2+), intersystem crossing by paramagnetic effect was mainly considered between (1)(ZnP)* and the [M(II)(edta)] complex. For the ZnMb-[M(II)(edta)] systems, the intramolecular ET reaction between the excited singlet state of (1)(ZnMb)* and the [Cu(II)(edta)] moieties provided the slower quenching rate constant, k(q) = 2.1 x 10(8) s(-1), compared with that of the ZnP(py)(edta) one. Kinetic studies also presented the efficient fluorescence quenching of the (1)(ZnMb)*-[Co(II)(edta)] dyad. Our study clearly demonstrates that wrapping of the ZnP cofactor by the apoprotein matrix and synthetic manipulation at the Mb surface ensure metal ion-sensitive fluorescent dynamics of ZnMb and provides valuable information to elucidate the complicated mechanism of the biological photoinduced ET reactions of hemoproteins.
authors.affiliation: Department of Chemistry, Faculty of Science, 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: Hiroe
authors.initials: H
authors.lastname: Kawahara
authors.forename: Miho
authors.initials: M
authors.lastname: Kitano
authors.forename: Satomi
authors.initials: S
authors.lastname: Shibata
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Murakami
authors.forename: Keiichi
authors.initials: K
authors.lastname: Tsukahara
mesh_terms: D002614:Chelating Agents / Q000737:chemistry*; D004492:Edetic Acid / Q000737:chemistry*; D007202:Indicators and Reagents; D007700:Kinetics; D008670:Metals / Q000737:chemistry; D009211:Myoglobin / Q000737:chemistry*; D010777:Photochemistry; D011166:Porphyrins / Q000737:chemistry*; D012996:Solutions; D013050:Spectrometry, Fluorescence; D013056:Spectrophotometry, Ultraviolet; D014867:Water / Q000737:chemistry; D015032:Zinc / Q000737:chemistry*
chemical_list: D002614:Chelating Agents; D007202:Indicators and Reagents; D008670:Metals; D009211:Myoglobin; D011166:Porphyrins; D012996:Solutions; D014867:Water; D004492:Edetic Acid; D015032:Zinc