Alterations in the chain dynamics of insoluble elastin upon proteolysis byserine elastases

The high temperature dielectric relaxations of purified and elastolized lig amentum nuchae elastin in the dry state have been investigated by thermally stimulated depolarization current spectrometry, with an equivalent frequen cy comprised between 10(-2) and 10(-3) Hz. A main relaxation mode, located close to 150 degreesC and attributed to the dielectric manifestation of a g lass transition, is found for all samples. After decomposition by the fract ional polarization method, the analysis of the high temperature mode shows the existence of two relaxation mechanisms: a cooperative one, associated w ith flexible zones of the protein, and an isoenthalpic one, corresponding t o more ordered and constrained zones. The activation parameters of the two mechanisms al-e dependent on the extent of elastolysis and on the nature of enzyme (pancreatic elastase vs leukocyte elastase). Both enzymes influence the dielectric behavior of elastin in a similar way: the activation enthal py maximum of the the relaxing units located in the flexible zones, charact eristic of the cooperative length, decreases with increasing hydrolysis. Mo reover, the isoenthalpic mechanism becomes cooperative at the highest exten t of elastolysis, which highlights release of constraints in ordered zones. Nevertheless, the differences found between the two enzymatic hydrolyses a re characteristic of distinct sites of cleavage in the elastin network. (C) 2001 John Wiley & Sons, Inc.