CONCENTRATION-DEPENDENCE OF HEMOGLOBIN MUTUAL DIFFUSION-COEFFICIENT

Laser correlation spectroscopy was used to measure the mutual diffusion coefficient, D, of human cyanomethemoglobin (Fe+++:CN) at varying protein concentrations. These measurements were made at 20.degree. C in a 0.1 M phosphate buffer solution at pH 7.0. For low protein concentrations, D = (6.43 .+-. 0.26) .times. 10-7 cm2/s and there was a near linear decrease from this value at higher concentrations. The linear relation between the diffusion coefficient and protein concentration allowed deduction of value of the linear frictional volume fraction coefficient, Kf = 7.75, and to extrapolate to Hb concentrations equivalent to that in the red blood cell where D was estimated to = 4.25 .times. 10-7 cm2/s. Various theoretical predictions of the dependence of the mutual diffusion coefficient on concentration were tested; the generalized Stokes-Einstein relation can be made to fit the high concentration data if a hard-sphere model was assumed and if a term involving a hydrodynamic interaction integral was included.