Figure 3.

Single turnover GTP hydrolysis rate of purified α_s isoforms. GTP hydrolysis of α_s-WT (■), α_s-Q170A (▴), and α_s-R258A (●) at 0°C is shown as the amount of phosphate (Pi) released as a function of time. The calculated catalytic rates (k_cat) also are shown. Each data point represents the mean ± SE of three experiments. Baseline counts at time zero ranged from 30 to 55% of maximum counts released. The majority of baseline counts is attributable to free inorganic phosphate contamination of the stock [³²P-γ]GTP.