Other Studies on Polypeptides

Krimm (1966) has called attention to experimental evidence which requires that antiparallel chains be present in polyglycine II. On the basis of the spacings in the powder diffraction pattern (Bamford et al., 1955), Crick and Rich (1955) had proposed a model for polyglycine II consisting of parallel polypeptide chains, each with a threefold screw axis, packed in a hexagonal array. Ramachandran et al. (1966) 

At normal temperatures, bands in the infrared spectrum of polyglycine II which can be associated with bonded CHj groups are consistent with the presence of suggested C—H- -0=C hydrogen bonds in a structure with parallel chains (Rama-chandran et ai, 1966), whereas bands associated with nonbonded CH2 groups require 

An examination of the structure of myoglobin (Krimm and Watson, 1967) indicated that C—H- -0=C hydrogen bonds are present in its a-helical segments. Therefore, although this type of bond is weaker than the N—H -0=C bond, it was suggested that the possibility of an attractive C—H - 0=C interaction should be incorporated into the principles underlying the structure of polypeptides and proteins. 

Poly-L-proline exists in two different conformations form I, which assumes a right-handed helix and has each peptide bond in the cis configuration (Traub and Shmueli, 1963) and form II, which is a left-handed helix and has its peptide bonds in the trans configuration (Sasisekharan, 1959 Cowan and McGavin, 1955). Isemura et at. (1968) have differentiated these two forms of poly-L-proline by characteristic far-infrared bands. Form I has two broad bands near 280 and 160cm and form II 

Swenson and Formanek (1967) have recorded spectra for H2O and DjO solutions of form n poly-L-proline as a function of temperature. The temperature range 

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