THERMAL-STABILITY AND REVERSIBILITY OF SECONDARY CONFORMATION OF ALPHA-CRYSTALLIN MEMBRANE DURING REPEATED HEATING PROCESSES

Reflectance FT-IR/DSC microspectroscopy was first used to study the st ructural conformation of alpha-crystallin membranes in the heating-coo ling-reheating cycle. The thermotropic transition and the changes in s econdary structure of alpha-crystallin membrane during heating and reh eating processes were investigated. A thermal transition ranging betwe en 50 and 70 degrees C with a midpoint at 60 degrees C for the alpha-c rystallin membrane was easily obtained from the three-dimensional plot s of the reflectance FT-IR spectra as a function of temperature. The s econdary structural components of the alpha-crystallin membrane were m odified step-by-step with the increase of temperature from 25 to 120 d egrees C, but restored to original values after cooling to 25 degrees C. During the heating process, the compositions of the alpha-helix, ra ndom coil and beta-sheet structure decreased with temperature, but the content of the beta-turn structure increased, however, all of them we re restored after cooling. The absence of significant alteration in th e secondary structures for the alpha-crystallin membrane before and af ter the first-heating process strongly suggests the high thermal stabi lity and reversibility of alpha-crystallin. Interestingly, the thermal behavior of the first-heated alpha-crystallin membrane during the reh eating process exhibited a unique thermal behavior with mio transition al temperatures at 35-50 and 55-70 degrees C. The reflectance FT-IR/DS C microscopic data indicated that alpha-crystallin in the membrane sta te had higher thermal stability and reversibility. (C) 1998 Elsevier S cience B.V. All rights reserved.