Figure 4.

(A) Rates of Meta II decay (I, ROS rhodopsin; II, rhodopsin in proteoliposomes) as monitored by fluorescence increase (see Materials and Methods). The maximum fluorescence, at the steady-state level, was used to normalize the progression of the signal. The ratio of the half-life of the Meta II decay for rhodopsin in proteoliposomes to that of the rhodopsin in ROS membrane was 1.16 ± 0.28 from three measurements. (B) G_T activation by light-activated rhodopsin in ROS membrane (I) and by rhodopsin in proteoliposomes (II). The first and the second negative-going spikes were the artifact of the light irradiation of the sample and the addition of GTP-γ-S, respectively. The rise of the fluorescence starting from time 0, in arbitrary units, indicated the formation of the Gα·GTP-γ-S (see Materials and Methods). The ratio of the initial rate of the reaction with the rhodopsin in proteoliposomes to that of rhodopsin in ROS membranes was 1.18 ± 0.24 from three measurements with equivalent amounts of rhodopsin.