muramidase and 1-1-3-3-tetramethylurea

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.

Topics: Calorimetry, Differential Scanning; Gels; Hot Temperature; Kinetics; Methylurea Compounds; Muramidase; Rheology; Solvents; Spectroscopy, Fourier Transform Infrared; Spectrum Analysis; Water

In this work, the gelation kinetics and fractal character of lysozyme gel matrices developed in tetramethylurea (TMU)-water media were investigated. Gelation times were determined from the temporal crossover point between the storage, G', and loss, G'', moduli, as a function of the binary solvent composition and of protein concentration. The inverse dependence of the upper limit of the linear viscoelastic region (gamma0) on protein concentration indicate that the lysozyme gels belong to the "strong link" kind, a gel category where interparticle links are stronger than intraparticle ones. Lysozyme gel fractal dimensions (Df) were determined from the analysis of rheological data according to a scaling theory by Shih et al. [Phys. Rev. A 42 (1990) 4772-4779] and were found to be compatible with a diffusion-limited cluster-aggregation kinetics (DLCA) for lysozyme gels formed at the TMU mass fraction in the binary organic-aqueous solvent, wTMU=0.9, and with a reaction-limited cluster aggregation kinetics (RLCA) for wTMU in the 0.6< or =wTMU< or =0.8 range.

Topics: Fractals; Gels; Kinetics; Methylurea Compounds; Muramidase; Rheology; Solvents; Surface Properties; Temperature; Time Factors; Water

Rheological properties of lysozyme viscoelastic matrices resulting from a sol-gel transition taking place in organic/aqueous media at room temperature were investigated. Gel-like structures, of transparent appearance, developed out of lysozyme (5.0 mmol/dm(3)) dispersed in tetramethylurea (TMU)/water binary mixtures, at TMU mass fraction (w) ranging from w(TMU) 0.6 to 0.9. The wide linear viscoelastic region (LVR) observed, up to strains of 10%, was invariant throughout the TMU concentration range investigated, indicating that the 3D structures of protein matrices, although fragile, are quite flexible and able to withstand great deformation before rupture. Storage (G') and loss (G") moduli continuously increased with increasing TMU concentration, the former at a greater rate, consequently leading systems to a decrease in the loss angle, tandelta. For gels developed out of binary systems at w(TMU)=0.9, creep curves revealed behaviour that very nearly approaches that of a perfect elastic solid. Although gelification under the experimental conditions employed is macroscopically accomplished in a time interval that does not exceed 24 h (for the gel developed out of the solvent mixture of lowest TMU concentration, w(TMU)=0.6), a slight decrease in loss angle can still be detected after that period. Such changes, however, have no effect on the LVR. Relaxation tests indicate that systems comprise at least two dynamically distinct contributions.

Topics: Elasticity; Gels; Linear Models; Methylurea Compounds; Muramidase; Rheology; Shear Strength; Solvents; Temperature; Thermodynamics; Time Factors; Viscosity; Water

Semi-solid viscoelastic matrices produced out of lysozyme in organic/aqueous media [tetramethylurea (TMU)/water] were characterized by small angle X-ray scattering (SAXS). The scattering curves were modeled in their form and interference factors. Radii of gyration of scattering particles were found to undergo a dramatic increase from 14 A in water to approximately 44 A in the matrices. Average correlation distances d=155 A were consistently verified for the scattering particles in the matrices, irrespective of solvent composition (in the 0.6

Topics: Animals; Chickens; Egg White; Elasticity; Female; Fourier Analysis; Methylurea Compounds; Models, Molecular; Muramidase; Protein Conformation; Scattering, Radiation; Solutions; Viscosity; Water; X-Rays