INFRARED SPECTRA AND STRUCTURE OF PROTEINS

Abstract

In order to throw some light on the interpretation of these spectra, observations have been made on amides and on nylon. In the former, the effects of hydrogen bonding have been found to be much more complex than was previously suspected in the region between $6\mu$ and $15\mu$; in nylon it has been found that raising the temperature causes shifts in the bands at $6\mu$ and $6.5\mu$ very similar to those attributed by others to the change in a protein from the $\alpha$ to the $\beta$ configuration. Since nylon is considered to remain in the $\beta$ configuration to high temperatures, this throws doubt on the correlation of these shifts with the transition from an $\alpha$ to a $\beta$ configuration. Experiments have been made on partially deuterating certain proteins by repeated immersion in heavy water. It is found that the bands at $3.08\mu, 3.28\mu, 6.5\mu, 8.1\mu$, and $14.2 \mu$ decrease in intensity, while increased intensity of absorption is observed at $4.15\mu$ and $6.96\mu$. Observations have also been made using polarized radiation with oriented materials. The significance of all these results on the interpretation of protein spectra will be discussed.Author Institution: Randall Laboratory of Physics, University of MichiganThe infrared spectra of 23 proteins of various types have been investigated in the range $2-15 \mu$ using a Perkin-Elmer double-beam spectrophotometer with a rock-salt prism. Although there is a considerable generation resemblance between the spectra of all the proteins, there are also marked differences, e.g., in the relative intensities of common bands and in their fine structure. Moreover, certain proteins exhibit bands not found in others. The extent to which differences in the spectra can be related to differences in amino-acid composition will be considered