Figure 4: Activation barriers for conformational dynamics and catalysis.

Barrier heights were determined at 25 °C from Eyring–Polanyi analyses by monitoring (a) apparent rate constants for Ap5a binding to Y171W based on fluorescence stopped-flow experiments, which yielded kinetic parameters of ΔH^sf=(62.1±2.8) kJ mol⁻¹ and ΔS^sf=−(4.7±0.2) J mol⁻¹ K⁻¹; and (b) conformational exchange dynamics for residue Thr89 of Y171W based on NMR line shape analysis. Eyring–Polanyi analysis in this case yields kinetic parameters of ΔH^LS=(68.6±4.7) kJ mol⁻¹ and ΔS^LS=(15.3±1.1) J mol⁻¹ K⁻¹. (c) Catalytic turnover values for the wild type (open circles) and Y171W (closed circles) AdK variants determined using a coupled assay³⁵. Eyring–Polanyi analysis yields kinetic parameters of ΔH^act_wt=(24.1±4.2) kJ mol⁻¹ and ΔS^act=−(120±20) J mol⁻¹ K⁻¹ for wild type, and ΔH^act_Y171W=(26.6±3.3) kJ mol⁻¹ and ΔS^act_Y171W=−(120±20) J mol⁻¹K⁻¹ for Y171W variant.