Homopolypeptides, random-coil

On the other hand, the deposition process is also important to prepare blend samples. A mixture of homopolypeptide solutions in which they take a random coiled structure are added into a poor solvent. For polypeptides, water is a poor solvent in general. If the hydration rate is different for each polypeptides, they form their preferred secondary structures by themselves and then do not blend with each other. On the basis of this assumption, in order to make the hydration at the same time, the solution is added to alkaline water. In this review, two kinds of quieting solvents such as water and alkaline water have been used. (Methods 1-4 and Method 5). Method 1 Helical polypeptide and (3-sheet polypeptide are dissolved in DCA and agitated... 

Early attempts used data obtained from homopolypeptides, such as poly(Lys), for their basis spectra [87, 88]. In the past fifteen years, approaches using data from globular proteins have emerged [18, 89-101]. Basically, a data base comprised of proteins with known secondary structure compositions is assembled and far UV CD spectra recorded. The choice of the proteins to be included is critical and various combinations have been examined. Mathematical matrix methods can be used to extract basis spectra which represent the contributions from the various secondary structures. Typically, four or five basis spectra can be obtained (corresponding to a helices, jj sheets, p turns, and random coil structures). In some approaches, such as those developed by Johnson and co-workers [11, 12, 51, 52, 102], separate basis spectra can be obtained for parallel and antiparallel p sheets. These basis spectra are then linearly combined to reconstruct the CD spectrum of the protein of interest The proportion of the basis spectra used to provide the best fit to the spectrum corresponds to the percentage of that secondary structure in the protein of interest Complete details of the mathematical algorithms that have been employed can be found elsewhere [10, 12, 17, 89, 103]. 

The random-coil CD spectrum of homopolypeptides displays a small positive elli-plicity at about 217 nm and a large negative eUipticity at about 198 nm. The CD spectra of random-coil or unordered homopolypeptides differ in two important regards from spectra of denatured proteins, namely ... 

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