Answer
If the solution contained an analog of GTP that cannot be hydrolyzed, such as guanosine-5'-O-(3-thiotriphosphate) (GTPγS), the microtubule in its shrinking phase would likely continue to depolymerize but at a slower rate than if only GDP was present.
Work Step by Step
This is due to the fact that while GTP-bound tubulin subunits can still form stable lateral bonds and add to the microtubule end, the inability to hydrolyze GTP-S avoids the instability of the lateral bonds that results from GTP hydrolysis.
During regular microtubule dynamics, GTP hydrolysis results in the release of a phosphate group, which weakens the lateral connections between nearby protofilaments and increases the likelihood that the microtubule will depolymerize. The lateral linkages between the GTP-S-bound tubulin subunits are stable in the presence of a GTP analog that cannot be hydrolyzed, offering some protection from depolymerization.
