Figure 2.

Time course of GTPγS binding to purified α_s. Bovine α_s-WT and -Q170A, each with a C-terminal hexahistidine extension, were purified from E. coli, and the rate of GTPγS binding for each was determined. α_s-WT (●) and -Q170A (▴) were incubated with 1 μM [³⁵S]GTPγS (≈10,000 cpm/pmol) at 20°C for varying times, and the amount of bound GTPγS was determined (18). Each data point is the mean ± SD of triplicate determinations. The apparent on rates for GTPγS (k_app) are shown (mean ± SE of six experiments).