Computer analyses of characteristic infrared bands of globular proteins

Infrared spectra of myoglobin, ribonuclease, lysozyme, α‐chymotrypsin, α‐lactalbumin, and β‐lactoglobulin A were obtained in deuterium oxide solution in units of absorbance versus wavenumber from 1340 to 1750 cm−1. The spectra were resolved into Gaussian components by means of an iterative computer program. Resolved characteristic absorption peaks for the two infrared active amide I′ components of antiparallel chain‐pleated sheets (β‐structure) were obtained. The characteristic amide I′ peaks of α‐helical regions and apparently unordered regions overlap in D2O solution. Absorptivity values for the resolved β‐structure peak around 1630 cm−1 were estimated on the basis of the known structure of ribonuclease, lysozyme, and β‐chymotrypsin. The β‐structure content of β‐lactoglobulin was estimated to be ca. 48% of α‐lactalbumin ca. 18%, and of αs‐casein close to zero. The results are in general agreement with conclusions drawn from circular dichroism and optical rotatory dispersion studies.