The properties of calmodulin at physiological temperature

Several of the physical properties of calmodulin are changed significantly upon increasing the temperature from 25 to 37°C. Among the observed changes are a minor increase in intrinsic viscosity, a decrease in molecular ellipticity in the peptide region, the development of a difference spectrum in the aromatic region, and an increase in the mobility of extrinsic fluorescent labels. Except for the latter case, the magnitudes of the changes are substantially reduced in the presence of Ca 2+ . The above observations are consistent with an expanded and less tightly organized structure of calmodulin at the higher temperature.