Fig. 1.

Simple model for local (vertical) and global (horizontal) conformational changes. The size of the circles reflects the magnitude of the overall isotropic rotational correlation time. The conventional analysis, which assumes that overall and internal motions are independent, is appropriate when only an single vertical pathway is present, and the corresponding correlation function is given in Eq. 6 with parameters in Eq. 7. If only the diagonal pathway is allowed, so that the overall rotational tumbling time and the local orientation of the vector of interest change simultaneously, the correlation function is still given by Eq. 6 but now with parameters in Eq. 8.