Infra-red spectra and structure of proteins

Abstract

The Infra-Red spectra of thirty-seven proteins have been observed between 650 and 3700 cm -1 . Several of the bands found common to them all had not been reported proviously and some other bands appear to be common only to those believed to exist in a folded configuration. A critical study of the exact positions of the bands near 1650 and 1550 cm -1 indicates that the frequency criteria developed for distinguishing a from β polypeptides cannot be reliably applied to proteins. Spectra obtained with polarized infra-red radiation confirms the view that in proteins where the polypeptide chain has a coiled (α) configuration, the NH stretching and the Co stretching bands have parallel dichroism and that the amide II band (near 1540 cm -1 ) has perpendicular dichroism: However, the counter part of the amide II band near 1240 cm -1 showed little dichroism in α proteins, but marked parallel dichroism in β proteins. The spectra of several deuterated proteins have been investigated; the results are of considerable value in making assignments of fundamental frequencies. Studies of deuterated silkworm gut using polarized infra-red radiation showed dichroic ratios of several key bands in proteins have been used to make quantitative tests of various polypeptide chain configurations which may exist in proteins. Satisfactory agreement was found in some cases with models based on X-ray diffraction data.