On the controversy over "fast" and "slow" helix-coil transition rates in polypeptides

The controversy over “fast” and “slow” helix-coil transition rates in polypeptides is discussed. The “slow” results are derived from the assumption that multiple NMR spectra of α-CH and NH groups arise from chemical exchange. In this paper it is shown that such spectra may be obtained without invoking chemical exchange. The multiplicity arises from the difference in helicity of amino acid residues near the ends of the chain by comparison with amino acid residues nearer the middle, and from a polydispersity in molecular weight. As a consequence of this analysis, support is given to the “fast” transition rates.