Interference of GTP hydrolysis in the mechanism of microtubule assembly: an experimental study.

Abstract

The interference of GTP hydrolysis in the mechanism of microtubule assembly was studied, following the model and theory previously published. Results from dilution experiments show that microtubules depolymerize faster below the critical concentration than expected with a reversible polymerization model. The experimental plot of flux vs. tubulin concentration exhibits a slope discontinuity at the critical concentration, in agreement with the theory. Theoretical points calculated by the Monte Carlo method can be fitted qualitatively to the data. A consequence of this peculiar dynamic behavior of microtubules is that the ratio of tubulin dissociation and association rate constants measured, respectively, below and above the critical concentration does not yield the true value of the critical concentration. The presence of GTP at microtubule ends is necessary to maintain the stability of the polymer.