Intrinsic viscosity of proteins

Protein charges that maintain the folded structure will be neutralized the electrostatic mteraction with guanidine chloride inducing by that an unfolded protein Also, mteraction occurs with the amino acids of the inner core of the protein inducing by that an irreversible unfolded state in presence of the denaturant. Equation 1.13 gives the relation that exists between the intrinsic viscosity of proteins (p) in presence nf 6 M guanidine chloride and the number (n) of amino acid residues per protein chain (Tanford elal. 1967). 

Hahn, D. K., and Aragon, S. R., Intrinsic viscosity of proteins and platonic solids by boundary element methods, J. Chem. Theory Comput, 2, 1416-1428 (2006). 

Effect of Intrachain Disulfide Bonds on Intrinsic Viscosities of Proteins in Concentrated Guanidine Hydrochloride (GuHCl) Solutions"... 

The ionic strength dependence of intrinsic viscosity is function of molecular structure and protein folding, ft is well known that the conformational and rheological properties of charged biopolymer solutions are dependent not only upon electrostatic interactions between macromolecules but also upon interactions between biopolymer chains and mobile ions. Due electrostatic interactions the specific viscosity of extremely dilute solutions seems to increase infinitely with decreasing ionic concentration. Variations of the intrinsic viscosity of a charged polyampholite with ionic strength have problems of characterization. 

Finally, for biological molecules that are macromolecules, such as most proteins, Eq. (4.23) can also be used to relate the relative viscosity to the intrinsic viscosity of the solution and the macromolecule concentration ... 

F ure 4.20 Variation of intrinsic viscosity of aqueous protein solutions with axial ratio and extent of solvation. Reprinted, by permission, from P. Hiemenz, Polymer Chemistry, p. 598. Copyright 1984 by Marcel Dekker, Inc. 

The intrinsic viscosity of native and denatured soy proteins have been measured (13). These values, which reflect the hydrodynamic properties oT the protein molecules at infinite dilution, are of little interest to us as far as functionality is concerned. What is of interest is the apparent viscosity of concentrated slurries. In these slurries, the intermolecular protein-protein interactions dominate and are primarily responsible for the observed viscosity behavior. 

EXAMPLE 4.4 Extent of Hydration of a Protein Molecule from Intrinsic Viscosity Measurements. Suppose an aqueous solution of a spherical protein molecule shows an intrinsic viscosity of 3.36 cm3 g 1. Taking p2 = 1.34 g cm 3 for the dry protein, estimate the extent of hydration of the protein. 

Finally, we note that both solvation and ellipticity can occur together. The contours shown in Figure 4.13a illustrate how various combinations of solvation and ellipticity are compatible with an experimental intrinsic viscosity. The particle considered in Example 4.4 has an intrinsic viscosity of 4.50 and was calculated to be hydrated to the extent of 0.60 g HzO per gram of protein. The same value of [17] is also compatible with nonsolvated ellipsoids of... 

FIG. 4.13 Intrinsic viscosity of a protein solution (a) variation of the intrinsic viscosity of aqueous protein solutions with axial ratio a/b and extent of hydration mlb/m2 (redrawn from L. Oncley, Ann. NY Acad. Sci., 41, 121 (1941)) (b) superposition of the [r ] = 8.0 contour from Fig. 4.13a and the f/f0 = 1.45 contour from Figure 2.9. The crossover unambiguously characterizes particles with respect to hydration and axial ratio. 

The stability of complexes formed in non-aqueous media against the destructive action of organic solvents has been studied (DMSO). The PAA-PVP polycomplex retains its compact structure up to 40 vol-% content of DMSO in the mixture with methanol (Fig. 16, curve 2) this follows from the low values of the intrinsic viscosity. A further increase of the DMSO content results in a sharp rise of the viscosity i.e. the complex dissociates. That the complex breaks down in pure DMSO is confirmed by the following facts the intrinsic viscosity of the PAA-PVP system is an additive function of the viscosity of individual polymers in this solvent while in methanol [ 7] of the PAA-PVP system is close to the viscosity of globular proteins. It is of interest that... 

In aciueous solutions containing high concentrations of LiBr or CaCb, the specific rotation of poly-E-proline II approaches [a] = —240°. Under these CH)nditions the intrinsic viscosity of the highly a.symmetric form II structure decreases markedly to values in the range of the globular proteins and it can be assumed that the configurational contribution to rotation of form II has been eliminated. 

Intrinsic Viscosities of Several Proteins and Polymers in Solutions ... 

The viscosity of solutions of globular proteins (which are more or less rigid) is only slightly affected by change in ionic strength. The intrinsic viscosity of semm albumin varies only between 3.6 and 4.1 cm g when the pH is varied between 4.3 and 10.5 and the ionic strength between zero and 0.50. 

FIG. 3 Variation of the intrinsic viscosity of long alkyl-modified polyacrylic acids as a function of the concentration of bovine serum albumin in the solvent. Solvent used for dilutions 30 mM borate buffer pH 9 and protein (top curves) or same buffer plus 0.3 M NaCl and protein (bottom curves). Black circles polymer modified with 4 mol% of C18 side groups squares polymer modified with 3 mol% of C12 groups cross-circles unmodified poly (sodium acrylate). (Reprinted with permission from Ref. 33. Copyright 1998 American Chemical Society.)... 

The distinction between poor and good solvent was introduced in the 1950s by Fox and Flory after experimental studies of the intrinsic viscosity of polymer solutions. These authors recognized that the viscosity varies in relation to the dependence of the chain sizes on temperature the poor solvent state is the state of a solution in which the chains have quasi-Brownian configurations. Systematic experiments have been made in this domain, for instance to determine the Flory temperature, but they have never given very precise results. Physicists are just now beginning to overcome the experimental and theoretical difficulties. Experiments have been made to show the existence of a collapse of the polymer chain, and certain authors have been prone to compare it with the coil-globule transition in proteins. 

The reduced specific viscosities of GDH in solution with 10" M GTP and 10 M NADH have been measured, and a value of intrinsic viscosity of [17] = 3.2 ml/g obtained by extrapolation to zero protein concentration (107). The transverse and axial rotary frictional coefficients of macroscopic models, similar to the physical model depicted in Fig. 2, were measured, and the viscosity calculated from these coefficients agrees with the measured value however, it is not possible to define whether the subunits adopt a staggered or eclipsed conformation, as viewed down the threefold axis, and other models may give the same result. 

Thus, the intrinsic viscosity of solvated spheres depends on the partial specific volume V2 of the solute, the specific volume vi of water, and the mass ratio r = mP/mi (degree of solvation) of both components in the interior of the sphere. Therefore, it is not possible to calculate the molar mass of a solvated sphere from the intrinsic viscosity alone. The intrinsic viscosities of spherical protein molecules are low, and for equal degrees of hydration are independent of the molar mass (Table 9-6). Admittedly, the proteins included in Table 9-6 are not perfectly spherical, since their coefficients of friction / are somewhat larger than those expected for a perfect sphere, o. 

In our laboratory, SEC-viscometry has been used to estimate the aspect ratio of proteins (81). This ratio, which describes the shape of proteins, is calculated from the Scheraga-Mandelkem P function (82). To determine this function, the intrinsic viscosity of the protein must be known accurately. Through the use of SEC-viscometry, proteins can be separated from interfering conformers and associated species, and intrinsic viscosities can be determined accurately. 

Finally, as the intrinsic viscosity of xanthan C was higher, its molecular weight can also be higher. It is quite possible that interactions between xanthan and bivalent ions and proteins can be different according to the polysaccharide chain length. 

To complicate matters still further, these protein molecules may assume different morphologies in different environments or solutions. Table 8 shows the intrinsic viscosities of various proteins where the intrinsic viscosity is defined as volume per mass of a given protein it may be seen that die molecular weights of proteins bear little relationsliip to the intrinsic viscosity. 

The intrinsic viscosity of globular proteins in a suitable buffer solution is independent of molecular weight This conclusion illustrates another important principle of polymer science proper interpretation of experimental data requires a v id theory. 

The sizes of the molecules were calculated based on these assumptions (1) these molecules exist in spherical form in aqueous condition (2) the intrinsic viscosity of the proteins in aqueous salt solutions is 3.4 cm/g.27... 

Mann (138) has found that the intrinsic viscosity of peanut protein in 10 M urea is increased by the reaction of the protein with terephthalyl dichloride. 

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