Dichroism of polypeptides

Johnson, W.C., Tinoco, I. Circular dichroism of polypeptide solutions in vacuum ultraviolet. 

Figure 1 The circular dichroism of polypeptides with different conformations. (—) a-helix, poly-L-lysine in water, pH 11.1,22°C ( ) /S-sheet, poly(Lys-Leu-Lys-Leu) in 0.5 M NaF at pH 7 ...

The characteristic ratio of polylA -ro-hydroxyethyl-L-glutamine) in water at 303 K is found to be 10 1, in agreement with results obtained by Brant and Flory [J. Am. Chem. Soc. 1965, 87, 2791) for four other polypeptides with -CH2—R side chains. The circular dichroism of polylA -m-hydroxyethyl-L-glutamine) under these conditions, where the polypeptide is in a statistical conformation, exhibits a positive band at 216 nm. 

Elliott, A. Infrared dichroism of synthetic polypeptides. Nature (Lond.) 172, 359—360 (1953). 

A photochromic polymer containing azobenzene units has also been prepared by modification of a naturally occurring microbial poly(E-L-lysine) (Scheme 5, Structure IX), and investigated by means of absorption and circular dichroism spectroscopy.1431 The structure of this polymer, however, does not correspond to those of polypeptides, which are poly(amide)s of a-amino acids, and therefore the results cannot be discussed in terms of the typical polypeptide structures (a-helix, P-structure, random coil) and their standard CD spectra. 

Blout ER, Carver JP, Shechter E (1967) ORD of Polypeptides and Proteins. In Snatzke G (ed) Optical Rotatory Dispersion and Circular Dichroism in Organic Chemistry. Heyden, London, p 224... 

In the case of m=2 in dimethylsulfoxide solution, the right-handed a-helical main chain conformation has been confirmed by the circular dichroism in the vibrational region (VCD). (A preliminary result of joint research with Professor T, Keiderling, University of Illinois at Chicago). By the VCD spectroscopy one can obtain information on the main chain conformation of polypeptides without any interference by the side-chain chromophores ( ). The VCD couplet... 

Absorption, circular dichroism and optical rotatory dispersion of polypeptides, proteins, prosthetic groups and biomembranes... 

Circular dichroism and absorption spectra of polypeptide conformations and prosthetic groups... 

In recent years, circular dichroism spectroscopy has been widely applied in investigations concerning the molecular structure of chiral polymers. It is a powerful tool for revealing the secondary structures of biological macromolecules, for instance of polypeptides, proteins, and nucleic acids in solution. An... 

The term inverse transition was first used in connection with the increase in order of the antibiotic stendomycin on raising the temperature (D.W. Urry and A. Ruiter, Conformation of Polypeptide Antibiotics. VI. Circular Dichroism of Stendomycin. Biochem. Biophys. Res. Commun., 38,800-806,1970). The term became specifically inverse temperature transition in relation to coacervation of elastin fragments that exhibited a phase separation with increased order on raising the temperature (B.C. Starcher, G. Saccomani, and D.W. Urry, Coacervation and Ion-Binding Studies on Aortic Elastin. Biochim. Biophys. Acta, 310, 481 86,1973, and D.W. Urry, B. Starcher, and S.M. Partridge, Coacervation of Solubilized Elastin Effects a Notable Conformational Change. Nature, 222,795-796,1%9). 

In order to address the question of whether or not the specific side chain conformation influences the main chain conformation, cylindrical brush polymers with poly-L-lysine (PLL) side chains were synthesized [88], Here, we will discussed in some detail the cylindrical brush sample CB-PLL55, which comprises 960 main chain repeat units and an average of 55 lysine repeat units in one side chain sample. Typically, PLL forms a random coil in aqueous solution In aqueous 0.5 M NaC104 solution, however, it is known to adopt one of the most prominent structures of polypeptides an a-helix (see also Sect 6.1) [89]. Upon reduction of the charge density by changing the pH to >9.8 and/or increasing the temperature or by addition of surfactant, a p-sheet structure is favored. Thus, cylindrical brushes with PLL side chains seemed to be ideal candidates for investigating the influence of a coil to a-helix to p-sheet transitimi of the side chains on the main chain conformation. Indeed, circular dichroism (CD) measurements confirmed that all three side chain conformations also occur in the side chains of cylindrical brush polymers (Fig. 18). 

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