EPR distance measurements in deuterated proteins.

One of the major problems facing distance determination by pulsed EPR, on spin-labeled proteins, has been the short relaxation time T(m). Solvent deuteration has previously been used to slow relaxation and so extend the range of distance measurement and sensitivity. We demonstrate here that deuteration of the underlying protein, as well as the solvent, extends the T(m) to a considerable degree. Longer T(m) gives greatly enhanced sensitivity, much extended distance measurement, more reliable distance distribution calculation and better baseline correction.