FIGURE 5.

Effects of GRK1₅₃₅H₆ variants on transducin (G_t) activation by Rho* and Meta II decay. Data for reactions without GRK1, with wt GRK1, with cross-linked T8C/N480C, and with ΔN19 are colored black, blue, purple, and green, respectively. Rate constants were calculated from three independent experiments, and data from a representative reaction are shown. (A) GRK1 inhibits activation of G_t by Rho*. The activation of G_t was monitored by the increase in its intrinsic tryptophan fluorescence because of nucleotide exchange catalyzed by Meta II (λ_excitation = 300 nm, and λ_emission = 345 nm). GTPγS (5 µM) was added to initiate the reaction after data had been recorded for 300 s. (B) GRK1 promotes Meta II decay. Meta II decay was measured by the increase of the intrinsic tryptophan fluorescence of Rho due to the release of the retinal chromophore (λ_excitation = 295 nm, and λ_emission = 330 nm).