Hemoglobin, diffusion molecular weight

Kofinas et al. (1996) have prepared PEO hydrogels by a similar technique. In this work, they studied the diffusional behavior of two macromolecules, cytochrome C and hemoglobin, in these gels. They noted an interesting, yet previously unreported dependence between the crosslink density and protein diffusion coefficient and the initial molecular weight of the linear PEGs. 

Based on the magnitude of diffusion constants for globular (i.e., spherical) protein molecules, one can estimate that proteins like hemoglobin (mass = 68 kDa diffusivity = 6.2 m /s X 10 ) can readily diffuse 20-30 micrometers within 10-20 seconds. By contrast, low-molecular-weight metabolites, such as glycine (mass = 75 diffusivity = 95 m /s X 10 ) and arginine (mass = 174 diffusivity = 58 m /s X 10 ), will rapidly traverse these distances in a few seconds or less. 

Sedimentation, used in conjunction with diffusion measurements, has been used for the determination of the molecular weights of macromolecules. At 20°C in a dilute aqueous solution, the sedimentation coefficient of hemoglobin, density 1.33 g/cm3, is 4.3 x 10"13 s. Its diffusion coefficient is 6.9 x 10 cm2/s. Calculate the molecular weight. How is this result affected by the hydration shell ... 

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