The enzyme soybean lipoxygenase (SLO) provides a prototype for deep tunneling mechanisms in hydrogen transfer catalysis. This work combines room temperature X-ray studies with extended hydrogen–deuterium exchange experiments to define a catalytically-linked, radiating cone of aliphatic side chains that connects an active site iron center of SLO to the protein–solvent interface. Employing eight variants of SLO that have been appended with a fluorescent probe at the identified surface loop, nanosecond fluorescence Stokes shifts have been measured. We report a remarkable identity of the energies of activation ( E a ) for the Stokes shifts decay rates and the millisecond C–H bond cleavage step that is restricted to side chain mutants within an identified thermal network. These findings implicate a direct coupling of distal protein motions surrounding the exposed fluorescent probe to active site motions controlling catalysis. While the role of dynamics in enzyme function has been predominantly attributed to a distributed protein conformational landscape, the presented data implicate a thermally initiated, cooperative protein reorganization that occurs on a timescale faster than nanosecond and represents the enthalpic barrier to the reaction of SLO.

The enzyme soybean lipoxygenase provides a prototype for deep tunneling mechanisms in hydrogen transfer catalysis. This work combines room temperature X-ray studies with extended hydrogen deuterium exchange experiments to detect a radiating cone of aliphatic side chains that extends from the iron active site of SLO to the protein-solvent interface. Employing eight variants of SLO, nanosecond fluorescence Stokes shifts have been measured using a probe appended to the identified surface loop. We report a remarkable identity of the enthalpies of activation for the Stokes shifts decay rates and the millisecond C-H bond cleavage step that is restricted to side chain mutants within the identified thermal network. While the role of dynamics in enzyme function has been predominantly attributed to a rapidly equilibrating protein conformational landscape, these new data implicate a rapid and cooperative protein quake as the origin of the thermal activation of SLO. A mechanism of catalysis is presented that combines a distributed conformational landscape with a long range and site-specific thermal quake.

Inverse vulcanisation stabilizes polysulfide chains through cross-linking. This research focuses on the incorporation of cyclosiloxane cross-linkers containing multiple alkene moieties, namely tetravinyl-tetramethyl-cyclotetrasiloxane (TVTSi) and pentavinyl-pentamethyl-cyclopentasiloxane (PVPSi). Both siloxanes underwent successful...