Albumin diffusion constant

The constant of proportionality, D, is the diffusion coefficient, and the negative sign is necessary because the net flux is from the region of high concentration to the region of low concentration. Table 23-1 shows that diffusion in liquids is 104 times slower than diffusion in gases. Macromole-cules such as ribonuclease and albumin diffuse 10 to 100 times slower than small molecules. 

Polnaszek and Bryant (1984a,b) measured the frequency dependence of water proton relaxation for solutions of bovine serum albumin reacted with a nitroxide spin label (4.6 mol of nitroxide per mol of protein). The relaxation is dominated by interaction between water and the paramagnetic spin label. The data were best fit with a translational diffusion model, with the diffusion constant for the surface water in the immediate vicinity of the nitroxide being five times smaller than that for... 

Most macromolecules when dissolved in salt solutions acquire charges that are shielded by an atmosphere of counterions. This ion atmosphere affects the diffusion coefficient of the macromolecule and hence the light-scattering time-correlation function. Electrolyte solutions are discussed in Chapters 9 and 13. Recent measurements of diffusion coefficients have been made by several groups. Lee and Schurr (1974) have studied poly-L-lysine-HBr. Schleich and Yeh (1973) have performed similar studies on poly-L-proline. Raj and Flygare (1974) have studied bovine serum albumin (BSA) and find that at high ionic strength and low pH the diffusion constant decreases. This they attribute to the expansion of the molecule. 

Since the rate constants of bimolecular diffusion-limited reactions in isotropic solution are proportional to T/ these data testify to the fact that the kt values are linearly dependent on the diffusion coefficient D in water, irrespective of whether the fluorophores are present on the surface of the macromolecule (human serum albumin, cobra neurotoxins, proteins A and B of the neurotoxic complex of venom) or are localized within the protein matrix (ribonuclease C2, azurin, L-asparaginase).1 36 1 The linear dependence of the functions l/Q and l/xF on x/t] indicates that the mobility of protein structures is correlated with the motions of solvent molecules, and this correlation results in similar mechanisms of quenching for both surface and interior sites of the macromolecule. 

Reactions of NO were also studied with the synthetic heme protein discussed earlier, namely the recombinant human serum albumin (rHSA) with eight incorporated TPPFe derivatives bearing a covalently linked axial base, were also investigated. The UV-vis absorption spectrum of the phosphate buffer solution at physiological pH showed absorption band maxima at 425 and 546 nm upon the addition of NO to form the nitrosyl species, which was also formed when the six-coordinate CO-adducts were reacted with NO gas. EPR spectroscopy revealed that the albumin-incorporated iron(II) porphyrin formed six-coordinate nitrosyl complexes. It was observed that the proximal imidazole moiety does not dissociate from the central iron when NO binds to the trans position. The NO-binding affinity P1 /2no was 1.7 X 10 torr at pH 7.3 and 298 K, significantly lower than that of the porphyrin complex itself, and was interpreted as arising from the decreased association rate constant (kon(NO), 8.9 x 10 M s" -1.5 x 10 M s ). Since NO-association is diffusion controlled, incorporation of the synthetic heme into the albumin matrix appears to restrict NO access to the central iron(II). ... 

Normal individuals excrete 31 mg of albumin in their urine daily. The studies of the physical and chemical properties of the urinary albumin have established that the urinary protein is identical to the blood protein. Both serum and urinary albumin have the same mobilities on free-starch electrophoresis and im-muno-electrophoresis. The sedimentation constants and the diffusion rates of the two proteins are similar, and their molecular weight must be of the order of 73,000. The two proteins react identically antigeni-cally. 

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