Conformational transitions of non-helical proteins effected by dodecyl sulfate: Circular dichroism of α1-acid glycoprotein, bence jones protein, carbonic anhydrase b, deoxyribonuclease, pepsinogen, and plasminogen

Abstract

Circular dichroism (CD) of serum α 1-acid glycoprotein, urinary Bence Jones protein, human carbonic anhydrase B, deoxyribonuclease from bovine pancreas, porcine pepsinogen, and plasminogen from human serum was tested in the absence and presence of 0.005–0.05 M sodium dodecyl sulfate. It was found that in all cases the CD spectra of these proteins were modified by the dodecyl sulfate into spectra indicating the presence of a moderate content of α-helix. The transitions were enhanced by addition of acid (pH 2.1–4.4) in all cases tested. Comparison of the various proteins with respect to the amount of reconstruction of the main chain conformation showed that the amount of helix formed depended on the amino acid composition of the protein. Rigidity due to cross-linking by disulfide bridges is the strongest deterrant to the conformational change of the main chain. The CD bands of the native proteins in the 250–350 nm spectral zone were extinguished by sodium dodecyl sulfate, and new weak bands were observed the positions of which corresponded approximately to those of the native proteins. In all cases, except the carbonic anhydrase B, the bands of thus denatured proteins were negative.