Double and single exponential kinetics of microtubule assembly in vitro

Abstract

1. 1. The kinetics of the microtubule protein assembly were studied in Mes buffer, pH 6.6, at 28°C. 2. 2. The assembly under above conditions follow a kinetic expression containing two exponential terms. The observed two rate constants depend on protein concentration, and are on the order of 10 −2 sec −1 and 10 −3sec −1. 3. 3. When CaCl 2 is added to the system in low concentration, the kinetic expression becomes single exponential. The observed rate constant is independent of protein concentration and its value is 5 × 10 −3 sec −1. 4. 4. It is concluded that the double exponential kinetics correspond to favorable assembly conditions, probably to a high extent of nucleation, whereas the single exponential kinetics is a slower process which occur under hindered assembly conditions.