Fig. 6.
Proton uptake and release upon activation of native rhodopsin in the presence of synthetic peptides derived from the C terminus of the Gtα subunit. The proton transfer was measured by changes in the 595-nm absorbance of BCP (see Materials and Methods). (A) Peptide Gtα(340–350) (NH2-IKENLKDCGLF-COOH, red traces) and the high-affinity analog Gtα(340–350)K341L (NH2-ILENLKDCGLF-COOH, blue traces) (19, 38). In both cases, the peptide affects net proton uptake (see text). (B) Plot of the final level of net proton uptake against peptide concentration; the solid lines are drawn to guide the eye. (C) (Upper) EPR spectra of 15 μM rhodopsin 227R1 in the dark state (black line) and after 15-s illumination (with a 515-nm cut-off filter, black dotted line). (Lower) Spectra as in Upper in the presence of 1 mM Gtα(340–350)K341L peptide.