Reprint of: Fourier Transform Infrared Study of Proteins with Parallel ß-Chains.

ABSTRACT

Deconvolved and second derivative Fourier transform infrared spectra of the proteins flavodoxin and triosephosphate isomerase have been obtained in the 1600 to 1700 cm-1 (amide I) region. To our knowledge these results provide the first experimental infrared data on proteins with parallel ß-chains. Characteristic absorption bands for the parallel ß-segments are observed at 1626-1639 cm-1 (strong) and close to 1675 cm-1 (weak). Previous theoretical studies based on hypothetical models with large, regular ß-sheets had suggested bands close to 1650 and 1666 cm-1. Our new assignments were confirmed by band area measurements, which yield conformational information in good agreement with results from X-ray diffraction data. The spectra were compared with corresponding spectra of concanavalin A and carboxypeptidase A. The first contains only antiparallel ß-segments, the second "mixed" ß-segments, with some strands lying antiparallel and others parallel. None of the observed amide I band frequencies assigned to parallel ß-chains occurs in the 1650 cm-1 region associated with helical segments.