  We report a dynamic light scattering study on protein suspensions of bovine
lens homogenates at conditions (pH and ionic strength) similar to the
physiological ones. Light scattering data were collected at two temperatures,
20 oC and 37 oC, over a wide range of concentrations from the very dilute limit
up to the dense regime approaching to the physiological lens concentration. A
comparison with experimental data from intact bovine lenses was advanced
revealing differences between dispersions and lenses at similar concentrations.
In the dilute regime two scattering entities were detected and identified with
the long-time, self-diffusion modes of alpha-crystallins and their aggregates,
which naturally exist in lens nucleus. Self-diffusion coefficients are
temperature insensitive, whereas the collective diffusion coefficient depends
strongly on temperature revealing a reduction of the net repulsive
interparticle forces with lowering temperature. While there are no rigorous
theoretical approaches on particle diffusion properties for multi-component,
non-ideal hard-sphere, polydispersed systems, as the suspensions studied here,
a discussion of the volume fraction dependence of the long-time, self-diffusion
coefficient in the context of existing theoretical approaches was undertaken.
This study is purported to provide some insight into the complex light
scattering pattern of intact lenses and the interactions between the
constituent proteins that are responsible for lens transparency. This would
lead to understand basic mechanisms of specific protein interactions that lead
to lens opacification (cataract) under pathological conditions.
