Protein fibrous, hydration

One of the key arguments for neutral site binding is the presence of (3-turns and associated conformations. This puts certain restrains on the structure of the fibrous protein. For elastin, conformations with bound calcium are likely to be inside-out with respect to hydrophobicity. Such structures are acceptable only for molecules functioning in a non-polar environment (cell-membranes) but not for a hydrated elastin fibre. Binding of calcium would stabilize a rigid inside-out conformation437. ... 

Amino acids of the general form, 1, are the monomeric molecules which are condensed to form the polypeptide chains of the fibrous and globular proteins. The naturally occurring molecules are the L-enantiomers, shown in 1 for chemical formulae see Fig. 19.1. D-amino acids can be synthesized and the individual L- or D-amino acids or the D,Lrracemates can be crystallized. All the common amino acids have been studied by neutron or X-ray crystal structure analysis (see Thble 14.1), in the anhydrous or hydrate forms, as hydrochlorides or hydrochloride hydrates. 

Crewther and Dowling at present take the view that the stability of a fibrous protein in a salt solution is determined largely by the number of sites available for hydration on ions bound by the fiber or absorbed as gegenions. The net charge on the fiber is important in that it determines the nature and number of gegenions absorbed. 

A variety of different experimental techniques has been used to investigate the hydration of fibrous proteins among them calorimetric > dielectric ( ) and dynamic-mechanical... 

Little information is however available in the literature on the specific volume of hydrated fibrous proteins. To the best of the authors knowledge, the only set of data published to date refers to hydrated keratin, was published by King (13), and later discussed by Rosenbaum (14). 

Volumetric data can be essential in the thermodynamic treatment of the "polymer-solvent" interaction process. The lack of them for many important fibrous proteins is due to the difficulty of measuring the density, at controlled temperature and hydration degree, for these systems. As far as elastin is concerned, it has been reported that when completely hydrated this protein has a negative and very large coefficient of thermal expansion (15), a result which has been interpreted as evidence of a hydrophobic character of the protein (16). 

The only other set of data available in the literature on density as a function of water content for a fibrous protein appears in the work of A. T. King (13) on hydrated wool at 25 C. The hydration range is similar to that of the present work, and the overall results are analogous at low levels of hydration the density of wool was found to remain approximately constant at higher water contents the density decreased approaching the values calculated on the basis of volume additivity. The maximum fractional volume change AV /V from King s data is about 5%,... 

This article concerns collagen fibers from rat tail tendon. The object is to confirm, improve or modify the proposed model by studying different collagen samples and secondly fibrous proteins such as the a keratin of human hair which exhibits similar hydration properties. 

This type of collagen has the advantage of illustrating the most recent structural data. It is necessary to review briefly this data to describe the proposed hydration model, and to aid in characterizing other samples of fibrous protein discussed later. 

The structure of certain fibrous proteins (wool and silk) has also been studied by the X-ray method. Fig. 138 giving Astbury s(i5) model for part of the unit cell in wool. Usually the proteins become denatured when one attempts to de hydrate them, a fact which has prevented successful elucidation of protein structure in many instances, although in a recent study it was found that there is a great deal of crystalline order in certain highly hydrated proteins (16). 

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