Small-angle x-ray scattering studies of thermally-induced globular protein gels

Small-angle X-ray scattering has been applied to gels formed by heating globular proteins, in aqueous solution, above their unfolding temperatures. A number of BSA gels, previously characterized by electron microscopy, have been studied, and, by setting up theoretical models for the scattering process, the X-ray data have been shown to be consistent with the microscope conclusions regarding network structure. It is concluded that the networks form by a linearly-directed aggregation of unfolded, disc-like, protein molecules, three-dimensional geometry being achieved by occasional branching, and/or cross-linking. Long-range inhomogeneities in network structure, easily observed by electron microscopy, and correlated with variations in pH or ionic strength, have an effect on X-ray scattering, and hence the x-ray method is sensitive not only to different network strand thicknesses, but to different degrees of uniformity as well.