title: Dielectric behavior of lysozyme and ferricytochrome-c in water/ethylene-glycol solutions.
abstract: This work deals with a dielectric study at radio frequencies of the influence at room temperature of two organic molecules, known as cryo-protectants, ethylene-glycol and glycerol, on conformational and dynamic properties of two model proteins, lysozyme (lys) from chicken egg-white and ferricytochrome-c (cyt-c) from horse heart. Cyt-c is a compact globular protein whereas lys is composed of two structural domains, separated by the active site cleft. Measurements were carried out at the fixed temperature of 20 degrees C varying the concentration of the cosolvent up to 90% w/w. From the analysis of the dielectric relaxation of the protein solution, the effective hydrodynamic radius and the electric dipole moment of the protein were calculated as a function of the cosolvent concentration. The data show that glycerol does not modify significantly the conformation of both proteins and cyt-c is also stable in the presence of ethylene-glycol. On the contrary ethylene-glycol strongly affects the dielectric response of lysozyme denoting a specific effect on its conformation and dynamics. The data are coherently interpreted hypothesizing that glycol molecule wedges between and separates the two domains of lys making them rotationally independent.
authors.affiliation: INFM-Dipartimento di Fisica, Università La Sapienza, I-00185 Rome, Italy. adalberto.bonincontro@uniroma1.it
authors.forename: A
authors.initials: A
authors.lastname: Bonincontro
authors.forename: S
authors.initials: S
authors.lastname: Cinelli
authors.forename: G
authors.initials: G
authors.lastname: Onori
authors.forename: A
authors.initials: A
authors.lastname: Stravato
mesh_terms: D000818:Animals; D002645:Chickens; D045424:Complex Mixtures / Q000737:chemistry; D045304:Cytochromes c / Q000737:chemistry*; D004553:Electric Conductivity; D019855:Ethylene Glycol / Q000737:chemistry*; D006736:Horses; D009113:Muramidase / Q000737:chemistry*; D009206:Myocardium / Q000201:enzymology; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D012996:Solutions; D013057:Spectrum Analysis / Q000379:methods*; D014867:Water / Q000737:chemistry*
chemical_list: D045424:Complex Mixtures; D012996:Solutions; D014867:Water; D045304:Cytochromes c; C421864:hen egg lysozyme; D009113:Muramidase; D019855:Ethylene Glycol