Additionally, the relevant RC angles were constrained in isomerization RCs (Supporting Information Figure ). Heavy atoms of the lysine substrate and the distance between the oxo ligand and the relevant hydrogen atom of lysine were also constrained and varied in increments of 0.05 Å for HAT RCs (Supporting Information Figure ). For rebound RCs, the distance between the carbon radical of the model substrate and oxygen of OH or halide was constrained and varied in increments of 0.1 Å (Supporting Information Figure ). High-energy structures along all RCs were used to obtain vibrational frequencies using gas-phase numerical Hessian calculations carried out at the corresponding levels of theory. The Hessian was computed using the central difference approach after 6N atomic displacements. The presence of an imaginary frequency along the RC confirmed characterization of high-energy structures along the RCs as transition states.