GLOBAL AND LOCAL CONFORMATIONAL TRANSITIONS DURING HEAT-INDUCED UNFOLDING OF LYSOZYME AND BACTERIAL RIBONUCLEASE IN SOLUTION AS REVEALED BYSPIN-LABEL ESR USING THE 2-MOTION MODEL

Transverse spin relaxation in solution was analyzed on the basis of a two-motion model for a covalently spin-labeled protein. For rapid moti on, an equation was derived linking the protein microdynamic parameter s such as tau(R)S(2) (product of the correlation time for protein over all tumbling and an order parameter) with the ESR line characteristics . Parameter S enables a more correct description of the conformational changes in lysozyme and bacterial RNase over 5-100 degrees C and pH 2 .5-7.0. The experimental temperature dependence of tau(R)S(2) revealed both local transitions and global melting. The thermal behavior of S was used to characterize different conformational states of protein.