  A theory is presented for lambda_C, the coefficient of the first-order
correction in the density of the collective diffusion coefficient, for protein
spheres interacting by electrostatic and adhesive forces. An extensive
numerical analysis of the Stokesian hydrodynamics of two moving spheres is
given so as to gauge the precise impact of lubrication forces. An effective
stickiness is introduced and a simple formula for lambda_C in terms of this
variable is put forward. A precise though more elaborate approximation for
lambda_C is also developed. These and numerically exact expressions for
lambda_C are compared with experimental data on lysozyme at pH 4.5 and a range
of ionic strengths between 0.05 M and 2 M.
