Figure 4.

Conformational heterogeneity in the dehydrogenase reaction mechanism. (a) In solutions of NADH or NADPH with a corresponding enzyme, the shortest-lifetime species (${\tau }_1$) exhibited rapid rotational diffusion, the intermediate-lifetime species (${\tau }_2$) displayed rotational diffusion consistent with a cone model, and the longest-lifetime species (${\tau }_3$) was associated with only the slow tumbling of the enzyme. (b) These configurations participate in the reaction mechanism of a dehydrogenase, in which the open ${\tau }_2$ form promotes the binding of substrate and the closed ${\tau }_3$ form facilitates hydride transfer. (c) Catalytically unproductive, abortive conformations are also possible, such as when reduced substrate binds alongside reduced cofactors. To see this figure in color, go online.