Introduction:
The aim of the present paper is investigation of the volume fraction dependence of the translational diffusion coefficient for some mammalian serum albumins in aqueous solutions.

Material and Methods:
The viscosity of bovine, equine, ovine and rabbit serum albumin aqueous solutions was measured at temperatures ranging from 5^oC to 45^oC and in a wide range of concentrations. The measurements were performed with an Ubbelohde-type capillary microviscometer.

Results:
Translational diffusion coefficient at infinitely dilute solutions D_o(T) can be calculated from generalized Stokes-Einstein equation if the hydrodynamic radius of albumin is known. It gives D_o(T) in the range from 3.5×10-11 m² /s (at 5^oC) to 10.2 10-11 m² /s (at 45^oC) for bovine serum albumin, from 3.59×10-11 m² /s (at 5oC) to 10.4 10-11 m² /s (at 45^oC) for equine serum albumin, from 3.42×10-11 m² /s (at 5^oC) to 9.92×10-11 m² /s (at 45^oC) for ovine serum albumin, and from 3.36×10-11 m² /s (at 5^oC) to 9.74×10-11 m² /s (at 45^oC) for rabbit serum albumin. Translational diffusion coefficient for higher concentrations D(T,φ) can be obtained from the relation: D(T,φ) = D_o(T)Η_o(T)/Η(T,φ), where φ denotes volume fraction and Ηo(T) and Η(T,φ) are viscosities of water and solution, respectively, at temperature T.

Conclusions:
The obtained results show that the translational diffusion coefficient decreases linearly with increasing volume fraction, when φ does not exceed the value of about 0.1. The dependence of the translational diffusion coefficient on volume fraction in a broader range of φ, i.e. from dilute to concentrated solutions, is nonlinear and can be described by a stretched exponential function.