Figure 2.

UV-vis absorbance spectra of PfTrpS. In the absence of substrate PfTrpS (20 μM) has an absorbance spectrum corresponding to E(Ain).³ Addition of 20 mM L-Ser yields a spectrum with λ_max = 350 nm. A similar peak with λ_max = 345 nm accumulates when L-Thr is added. This shift may reflect a mix of signals with α-ketobutyrate (λ_max = 319 nm) formed from the fast deamination of L-Thr. The additional peak at ~425 nm corresponds to a small population of the E(Aex₁) intermediate.