title: Solvent-induced lysozyme gels: effects of system composition and temperature on structural and dynamic characteristics.
abstract: The gelation process of lysozyme in water/tetramethylurea in the presence of salt was investigated as a function of temperature and system composition by rheology, infrared spectroscopy, and microcalorimetry. Times and temperatures of gelation were determined from the variation of the storage (G') and loss (G'') moduli. It was found that gelation times follow exponential decays with both protein and tetramethylurea (TMU) concentrations and with temperature. The activation energy for the overall process shows a linear dependence on TMU mass fraction. A strongly increased beta-sheet content and reduced alpha-helix occur with the increase of TMU concentration in the binary solvent. Also, a linear decrease of lysozyme denaturation temperature and enthalpy on TMU concentration is found for the TMU mass fraction up to 0.5, above which no denaturation signal can be detected.
authors.affiliation: Departamento de Química Fundamental, Instituto de Química, Universidade de São Paulo, Caixa Postal 26077, CEP 05513-970 São Paulo, SP, Brazil.
authors.forename: Marcelo A
authors.initials: MA
authors.lastname: da Silva
authors.forename: Imad A
authors.initials: IA
authors.lastname: Farhat
authors.forename: Elizabeth P G
authors.initials: EP
authors.lastname: Arêas
authors.forename: John R
authors.initials: JR
authors.lastname: Mitchell
mesh_terms: D002152:Calorimetry, Differential Scanning; D005782:Gels / Q000737:chemistry; D006358:Hot Temperature; D007700:Kinetics; D008782:Methylurea Compounds / Q000737:chemistry; D009113:Muramidase / Q000737:chemistry*; D012212:Rheology; D012997:Solvents / Q000737:chemistry; D017550:Spectroscopy, Fourier Transform Infrared; D013057:Spectrum Analysis; D014867:Water / Q000737:chemistry
chemical_list: D005782:Gels; D008782:Methylurea Compounds; D012997:Solvents; D014867:Water; C004168:1,1,3,3-tetramethylurea; D009113:Muramidase