title: Extractive solubilization, structural change, and functional conversion of cytochrome c in ionic liquids via crown ether complexation.
abstract: This article reports on the extraction behavior of heme proteins from an aqueous phase into ionic liquids (ILs) with dicyclohexano-18-crown-6 (DCH18C6), and the structure-function relationship of cytochrome c (Cyt-c) dissolved in ILs. We have found that DCH18C6 enables transfer of Lys-rich proteins into ILs via supramolecular complexation. The hydrophobicity and functional groups of ILs have a great influence on protein partitioning, and a hydroxyl group-containing IL with DCH18C6 is capable of the quantitative partitioning of Cyt-c. On the other hand, protein transfer using conventional organic solvents is negligibly small. UV-visible, CD, and resonance Raman spectroscopic characterizations indicate that the sixth ligand Met 80 in the heme group of the Cyt-c-DCH18C6 complex in IL is replaced by other amino acid residues of the peptide chain and that a non-natural, six-coordinate, low-spin ferric heme structure is induced in IL. Solubilization of Cyt-c in IL causes the environmental change of the heme vicinity of Cyt-c, which triggers the functional conversion of Cyt-c from an electron-transfer protein to peroxidase. The Cyt-c-DCH18C6 complex in IL provides remarkably high peroxidase activity compared with native Cyt-c, because of enhancement of the affinity for H2O2.
authors.affiliation: Division of Environment and Radiation Sciences, Nuclear Science and Engineering Directorate, Japan Atomic Energy Agency, Tokai-mura, Ibaraki, 319-1195, Japan. shimojo.kojiro@ jaea.go.jp
authors.forename: Kojiro
authors.initials: K
authors.lastname: Shimojo
authors.forename: Noriho
authors.initials: N
authors.lastname: Kamiya
authors.forename: Fumito
authors.initials: F
authors.lastname: Tani
authors.forename: Hirochika
authors.initials: H
authors.lastname: Naganawa
authors.forename: Yoshinori
authors.initials: Y
authors.lastname: Naruta
authors.forename: Masahiro
authors.initials: M
authors.lastname: Goto
mesh_terms: D002384:Catalysis; D043844:Crown Ethers / Q000737:chemistry*; D045304:Cytochromes c / Q000737:chemistry*; D004579:Electron Transport; D006418:Heme / Q000737:chemistry / Q000378:metabolism; D006861:Hydrogen Peroxide / Q000494:pharmacology; D007477:Ions; D010084:Oxidation-Reduction; D010455:Peptides / Q000737:chemistry / Q000378:metabolism; D009195:Peroxidase / Q000737:chemistry / Q000378:metabolism; D011506:Proteins / Q000737:chemistry / Q000378:metabolism; D012995:Solubility; D012996:Solutions / Q000737:chemistry*; D013057:Spectrum Analysis; D013997:Time Factors
chemical_list: D043844:Crown Ethers; D007477:Ions; D010455:Peptides; D011506:Proteins; D012996:Solutions; D006418:Heme; D045304:Cytochromes c; D006861:Hydrogen Peroxide; D009195:Peroxidase