Table 2. Melting temperatures of apo- and acylenzyme conjugates of CTX-M9 and top mutants. Melting temperatures were determined in increments of 0.5 °C. All enzymes showed a 3–4 °C destabilization in the acylenzyme state (measured by pre-incubating enzyme with meropenem); T165W shows a reproducible 1.5–2 °C stabilization compared to the other enzymes, while L48A and S281A show a very mild but consistent destabilization of 1–1.5 °C. Thermal melting curves are given in Fig. S6. Uncertainties were limited to 0.5 °C by the precision of the instrument used; agreement between multiple experimental replicas was exact to within this limit.

	CTX-M9	L48A	T165W	S281A
Apo enzyme	48.0 ± 0.5 °C	47.5 ± 0.5 °C	49.5 ± 0.5 °C	47.0 ± 0.5 °C
Acylenzyme	45.0 ± 0.5 °C	43.5 ± 0.5 °C	46.5 ± 0.5 °C	43.5 ± 0.5 °C