Circular dichroism of the “random” polypeptide chain

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Abstract
The circular dichroism (CD) spectrum of an unordered polypeptide chain does not correspond, as has been assumed heretofore, to that of a charged chain such as poly‐L‐glutamic acid or poly‐L‐lysine. The latter have been shown to have locally ordered structures with characteristic CD spectra. We have now obtained CD spectra of the unordered forms of the above synthetic, polypeptides, as well as of two fibrous proteins (collagen and feather keratin) and a globular protein (myoglobin). These spectra are all similar to that of unordered polyproline, having a negative band in the vicinity of 2000 mμ and no additional bands at longer wavelengths. The lack of structural uniqueness of the unordered polypeptide chain is emphasized by these studies.