Solvent-slaved protein motions accompany proton but not hydride tunneling in light-activated protochlorophyllide oxidoreductase.

H(+) but not H(-): The reduction reaction of protochlorophyllide catalyzed by protochlorophyllide oxidoreductase features solvent-slaved motions that control the proton- but not the hydride-tunneling mechanism. These motions imply a long-range dynamic network from the solvent to the enzyme active site that facilitate proton transfer (see picture, left). Motions for hydride transfer are more localized and are not slaved by the solvent (see picture, right).