NMR EVIDENCE OF FORMATION OF CYCLOCYSTINE LOOPS IN PEPTIDE MODELS OF THE HIGH-SULFUR PROTEINS FROM WOOL

We report that in peptide models of the high sulfur proteins of the ma trix from wool a disulfide bond forms between two sequential Cys-resid ues as a result of a simple oxidation procedure. This tiny cyclocystin e loop manifests itself in many ways in H-1 NMR spectra. The formation of the loop is accompanied, as expected, by conversion of the Cys-Cys peptide bond from its usual trans-configuration into the energeticall y less favorable cis-configuration. Possible consequences of the forma tion of cyclocystine loops for the elasticity of the network of the ma trix are discussed.