Extractive solubilization, structural change, and functional conversion of cytochrome in ionic liquids via crown ether complexation

Shimojo, Kojiro; Kamiya, Noriho*; Tani, Fumito*; Naganawa, Hirochika; Naruta, Yoshinori*; Goto, Masahiro*

Analytical Chemistry, 78(22), p.7735 - 7742, 2006/11

https://doi.org/10.1021/ac0612877

We have found that dicyclohexano-18-crown-6 (DCH18C6) enables transfer of Lys-rich proteins into ionic liquids (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-. UV-Vis, CD, and resonance Raman spectroscopic characterizations indicate that the sixth ligand Met 80 in the heme group of the Cyt--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- in IL causes the environmental change of the heme vicinity of Cyt-, which triggers the functional conversion of Cyt- from an electron-transfer protein to peroxidase. The Cyt--DCH18C6 complex in IL provides remarkably high peroxidase activity compared with native Cyt-, because of enhancement of the affinity for HO.