Proteins random coils

Random coil proteins (e.g., casein) IgG hydrolysis products Cell-bound antigen... 

The dimensions of protein random coils are calculated for a variety of proteins of known amino acid sequence. Glycine and proline contribute to reducing the dimensions of random coil proteins. Branched side chains expand the chain only slightly more than unbranched side chains. Side chains represented as structured to the y position are compared with structureless representations. It is demonstrated that the two approaches give comparable chain dimensions. The effect of sequence is investigated. 

The usefulness of infrared spectroscopy of proteins and membranes is increased when spectra of dry films are compared with those taken in deuterium oxide. Exchange of protons for deuterons can affect both the amide I and amide II bands. For randomly coiled proteins in D20 the amide I band is shifted down by about 10 cm."1 but for many proteins D20 does not affect the frequency of the carbonyl stretch of either the ft structure or the a-helix. In addition, upon complete exchange the amide... 

Qu, Y., C.L. Bolen, and D.W. Bolen (1998). Osmolyte-driven contraction of a random coil protein. Proc. Natl. Acad. Sci. USA 95 9268-9273. 

By elaboration of their intrinsic viscosity data according to the Stockmayer and Fixman equation, Tanford et al. have arrived at the following average value for the characteristic ratio of randomly coiled proteins (r yjnP 5.0. ... 

More recently Lapanje and Tanford (59) have reported osmotic pressure measurements for reduced protein polypeptide chains in 6M guanidine hydrochloride. Second virial coefficient data and intrinsic viscosity data are combined by these authors to yield unperturbed dimensions of randomly coiled proteins. The result is assentially identical with that obtained earlier from viscosity data alone. 

The shapes of solutes are also important in their retention behavior it has been shown that DNA restriction fragments (rod-shaped) have Km values that are more sensitive to molecular weight than those obtained with denatured (random-coil) proteins. In fact, the SEC parameter governing the retention is the hydrodynamic volume of the solute, which is related to its radius of gyration, Rg. The molecular weight of a solute is related to its radius of gyration by Eq. 14.12 ... 

The degree of swelling of a random coil depends on the quality of the solvent. While 6 M GuCl or 8 M urea are moderately good solvents for randomly coiled proteins [2,3], water is certainly a rather bad one for denatured proteins, as demonstrated by the compact structure of the native state and suggested by their strong propensity to aggregate when unfolded in water, after heat denaturation for example. The problem is to know whether the size of denatured pro-... 

When using molar mass as the calibration parameter, one has to consider the shape of macromolecules in solution during the data evaluation e.g., it is not possible to calculate directly the molar mass of the randomly coiled proteins from the calibration curve obtained by means of the globular proteins. 

Conformational changes may also be detected by c.d. The denaturation of a-lactalbumin with guanidinium hydrochloride was studied by Kuwajima. The unfolding process, which involves three stages with an a-helical intermediate state, was followed by c.d. and difference spectra. Similarly, Takahashi et al. noted that disulphide-reduced ribonuclease A had a c.d. spectrum different from either the native or random coil protein. The reoxidation of the reduced enzyme (which results in recovery of activity) was followed by c.d. and it was shown that the change in a-helix was more rapid than that in j -structure. 

Resonances that are indicative of a structured (non-random coil) protein... 

Figure 45 Schematic representation of protein structure at a fluid interface. 1 = flexible, random-coil proteins 2 = globular, highly structured proteins. The arrow denotes increasing protein concentration.

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