Figure 7.

Location of the residues modified to form the high Q mutant V49A/I119T/T121S/A126T, with the relevant residues marked with red lettering. Other residues that are important to the photochemical properties or proton translocation process are also shown. The proton channel is shaded. The contours of the electrostatic difference map associated with the quadruple mutation are shown in the background. The key electrostatic impact of the mutation is to increase negative charge in the Asp-85 (D85) and Asp-212 (D212) region, which stabilizes the protonation of D85 and prolongs the yield and lifetime of the O state. The V49A component of this mutation also preferentially stabilizes the 9-cis conformation. Contour lines are drawn at the following energies (J/mol): ±1, ±6, ±21, ±49, ±96, ±170, ±260, ±390, ±560, ±760, ±1000, ±1300, ±1700, ±2100, ±2600, ±3100, ±3800, ±4500, ±5200, ±6100.