Hemoglobin diffusion constant

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. 

Sickle-cell-anemia hemoglobin is closely similar to normal adult human hemoglobin in most of its properties. The two proteins have approximately the same sedimentation and diffusion constants,... 

Computing the radius of hemoglobin. Assume that hemoglobin is a sphere. Compute its radius from its diffusion constant in Table 18.1. 

R. A. Alberty and G. G. Hammos, J. Phys. Chcm.y 62, 154 (1958), have shown that the very fast specific rate constants observed for this reversible reaction are compatible with a diffusion-controlled rate such that every collision of a fumarate ion with an active site leads to reaction. This is apparently true also for the combination of NO with iron hemoglobin and H2O2 with yeast peroxidase. 

The helium is inert and insoluble in lung tissue and blood, and equilibrates quickly in unobstructed patients, indicating the dilution level of the test gas. Acetylene, on the other hand, is soluble in blood and is used to determine the blood flow through the pulmonary capillaries. Carbon monoxide is bound very tightly to hemoglobin and is used to obtain diffusing capacity at a constant pressure gradient across the alveolar-capillary membrane. 

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