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. 1999 Apr 27;96(9):4898–4903. doi: 10.1073/pnas.96.9.4898

Figure 1.

Figure 1

Gt-derived peptides increase the formation of metarhodopsin II (MII) photointermediate. At pH 7.9, 1.5°C flash photolysis of rhodopsin (indicated by the flash symbol) predominantly produces the MI photoproduct (λmax = 478 nm), which is in a dynamic equilibrium with a small proportion of MII (λmax = 380 nm, isosbestic point for MI/MII at λ = 417 nm). Heterotrimeric Gt or Gt mimetic peptides shift the MI–MII equilibrium toward MII in a concentration-dependent manner to produce extra MII. The amount of extra MII was monitored by UV/Vis spectroscopy. Traces represent readings of a 380–417 nm absorbance difference (ΔAbs) from the samples containing 10 μM (A and C) or 5 μM (B) of washed-rod outer-segment membranes as described (19). Extra MII produced by the indicated concentrations (mM) of Gtγ(50–71)farnesyl (A), Gtα(340–350) (B), and the Gtα(340–350) high-affinity analog (VLEDLKSCGLF) (C). Amplitudes of the extra MII signals from A–C are plotted vs. peptide concentration (D, ΔAbs at saturation taken from C).