Fig. 4.

(A) The pH titration of the Schiff base in the purified GtACR1_E68Q mutant by measuring formation of an M-like state (the maximum at 390 nm at high pH in the dark). (Inset) The absorption spectrum of this state obtained by summation of the difference spectrum between pH 11 and pH 8 with the properly scaled spectrum of the unphotolysed state at pH 7.4. (B) The pH dependence of the maximal absorption wavelength for the E68Q mutant and WT. (C) Light-induced absorption changes of the E68Q mutant at 590 nm and 460 nm, associated with biphasic decay of K and formation of L. The incomplete K decay in submillisecond time ranges suggest establishment of equilibrium concentrations of K and L from a reversible K⇔L conversion. (D) Comparison of L-to-M transitions in WT and the mutant.