FIG. 5.

Inhibition of the Cdc25^Mm285-stimulated dissociation rate of Ras-3′mdGDP by Ras(E37G/D119N). Addition of Ras(E37G/D119N)-GDP to a mixture of 100 nM Ras-3′mdGDP, 100 nM Cdc25^Mm285, and 20 μM GDP in standard buffer at 20°C inhibited the Cdc25^Mm285-stimulated dissociation rate in a concentration-dependent manner. Replacement of the excess of 20 μM GDP (●) by 200 μM GDP (□) or 2 mM GDP (■) abrogated the inhibitory action of Ras(E37G/D119N). The Cdc25^Mm285 preparation used in this experiment was 35% less active than the one used in Fig. 3. k_obs, observed dissociation rate constant.