Fig. 4.

(A) Transducin activation by MUV and its counterion mutant, E108Q. The reaction was illuminated for 1 min, and then aliquots were removed and assayed for GTPγS bound to transducin. The solid lines represent the regression fit to the initial rate for each curve. (B) The decay of the active state of MUV and E108Q after illumination. The pigments were exposed to 1 min of illumination in the absence of transducin. Aliquots were added to transducin with a delay of 1–30 min and incubated for an additional 10 min in dark before assaying; a delay of 0 min was achieved by illuminating in the presence of transducin.