We have previously shown that both Smg GDP dissociation stimulator (GDS) and mammalian Cdc25 (mCdc25) stimulate the GDP/GTP exchange reaction of Ki- Ras and that Smg GDS is active only on the post-translationally lipid- modified form of Ki-Ras, whereas mCdc25 is active on both the lipid-modified and unmodified forms but is more active on the lipid-modified form. In the present study, we compared more detailed kinetic properties of Smg GDS and mCdc25 by use of the lipid-modified form of Ki-Ras as a common substrate. Both Smg GDS and mCdc25 stimulated the dissociation of GDP from Ki-Ras and formed the stable binary complex with Ki-Ras. In the presence of guanosine 5'-(3-O-thio) triphosphate (GTPγS), the stable ternary complex of Smg GDS- GTPγS-Ki-Ras was produced, whereas GTPγS induced the dissociation of mCdc25 from mCdc25-Ki-Ras complex, yielding GTPγS-Ki-Ras. mCdc25 stimulated the dissociation of GDP from both the membrane-bound and soluble forms of Ki- Ras, whereas Smg GDS was far less active on the membrane-bound form than on the soluble form. Moreover, Smg GDS translocated the GTPγS-bound form of membrane-bound Ki-Ras to the soluble fraction as the stable ternary complex of Smg GDS-GTPγS-Ki-Ras, whereas mCdc25 did not show this activity. These results suggest that Smg GDS and mCdc25 play different roles in the regulation of Ki-Ras.
|Number of pages||7|
|Journal||Journal of Biological Chemistry|
|Publication status||Published - 27-05-1994|
All Science Journal Classification (ASJC) codes
- Molecular Biology
- Cell Biology