Time dependence of the concentration of photointermediates and proton release seen after photolysis of rhodopsin mutants E134R/R135E and E134Q. Curves (solid, E134R/R135E; dashed, E134Q) show the relative concentration of photointermediates that appear after photolysis, and points (+, E134R/R135E; o, E134Q) show proton changes associated with the pigments after photolysis (proton release signal at 690 ms was the same as at 10 ms, data not shown). Although the concentrations of E134R/R135E and E134Q photointermediates have time dependence very similar to those observed for wild type rhodopsin, in these mutants only proton release by the protein is seen (rather than the uptake seen for wild type rhodopsin).