Previous studies of a thermophilic 'alcohol dehydrogenase (ht-ADH) demonstrated a range of discontinuous transitions at 30 degrees C that include catalysis, kinetic isotope effects, protein hydrogen deuterium exchange rates, and intrinsic fluorescence properties. Using the Forster resonance energy: transfer response from-a Trp-NADH donor-acceptor pair in T-jump studies of ht-ADH we now report Microsecond protein motions that can be directly related to active site chemistry. Ditto distinctive transients are observed: a slow, kinetic process lacking a temperature break, together with a faster transient that is only detectable above 30 degrees C. The latter establishes a link between enzyme activity and microsecond protein motions near the cofactor binding site, in a region distinct from a previously detected protein network that communicates with the substrate binding site. Though evidence of direct dynamical links between microsecond protein motions and active site bond cleavage events is extremely rare, these studies highlight the potential of T-jump measurements to uncover such properties.