Lysozyme viscoelastic matrices in tetramethylurea/water media:: a small angle X-ray scattering study

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 Angstrom in water to approximately 44 Angstrom 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 less than or equal to w(TMU) less than or equal to 0.8 range), in contrast to what is observed in water (d = 62 Angstrom). At w(TMU) = 0.9, however, a slight increase in wR(g) (to R-g = 49 Angstrom) leads to interdigitation with the apolar prevailing medium of the matrix leading to the loss of the interference effect. Low dimensionality derived from the modeling procedure could be taken to indicate mass fractal character of the unfolded species, although polydispersion of samples could also have some contribution to that result. Despite the very significant shape distortion of the unfolded protein forms in the matrices, they still retain considerable globular character, as indicated by the Kratky plots obtained. The morphological results obtained in this work are compatible with the dynamical behavior displayed by the systems. (C) 2002 Elsevier Science B.V All tights reserved.