FIG. 4.

Inhibition of the Cdc25^Mm285-stimulated dissociation rate of Ras-3′mdGDP by addition of Ras(D119N). (A) The dissociation of 100 nM p21-3′mdGDP in the presence of 20 μM GDP in standard buffer at 20°C (+) was stimulated to 0.0018 s⁻¹ by addition of 163 nM Cdc25^Mm285 (○). This stimulation was inhibited by the addition of 2 μM Ras(D119N)-GDP (●), but this inhibition was counteracted by the addition of 20 μM XDP (□), 200 μM GDP (■), or 2 mM GDP (▵). (B) Different representation of measurements performed as described for panel A. Addition of Ras-GDP (○) hardly affected the Cdc25^Mm285-stimulated dissociation rate of Ras-3′mdGDP, whereas addition of Ras(D119N)-XDP (⧫) or Ras(D119N)-GDP (●) inhibited this stimulation in a concentration-dependent manner. Replacement of the excess of 20 μM GDP (○, ●, and ⧫) by 20 μM XDP (▿), 200 μM GDP (◊), or 2 mM GDP (□) abrogated the inhibitory action of Ras(D119N).