Microtubule assembly of isotypically purified tubulin and its mixtures.

Numerous isotypes of the structural protein tubulin have now been characterized in various organisms and their expression offers a plausible explanation for observed differences affecting microtubule function in vivo. While this is an attractive hypothesis, there are only a handful of studies demonstrating a direct influence of tubulin isotype composition on the dynamic properties of microtubules. Here, we present the results of experimental assays on the assembly of microtubules from bovine brain tubulin using purified isotypes at various controlled relative concentrations.

Directed binding: a novel physical mechanism that describes the directional motion of two-headed kinesin motor proteins.

We propose a novel physical mechanism to describe the mode of processive propagation of two-headed kinesin motor proteins along microtubule (MT) filaments. Binding and unbinding of the kinesin heads to and from the MT filament play a crucial role in producing movement. The chemical energy of adenosine triphosphate hydrolysis is used in large part for the unbinding process of kinesin from the MT filament.

Elementary arguments that the Wu-Austin Hamiltonian has no finite ground state (the search for a microscopic foundation of Frölichs theory).

The Wu-Austin Hamiltonian as the basis for deriving Fröhlichs rate equations from a microscopical point of view has been investigated. In addition to an earlier paper we show in a very easy manner that this or similar Hamiltonians have no lower bound and are therefore unphysical. The perturbation expansion which is the tool to derive Fröhlichs rate equations with this Hamiltonian is not converging.

Microtubules: strange polymers inside the cell.

This paper provides a consistent approach (within a one-dimensional approximation) to the description of the evolution of the microtubule length at both low- and high-density concentrations. We derive general master-type equations which are based on the key chemical reactions involved in the assembly and disassembly of microtubules. The processes included are: polymerization and depolymerization of a single protein dimer, catastrophic disassembly affecting an a piori arbitrary number of dimers, and a rescue event.

Models of assembly and disassembly of individual microtubules: stochastic and averaged equations.

In this paper we present solutions of the master equations for the microtubule length and show that the local probability for rescues or catastrophes can lead to bell-shaped length histograms. Conversely, as already known, non-local probabilities for these events result in exponential length histograms. We also derive master equations for a stabilizing cap and obtain a new boundary condition which provides an explanation of the results obtained in dilution and cutting experiments.

A chemical kinetics model for microtubule oscillations.

A model for microtubule oscillations is presented based on a set of chemical reaction equations. The rate constants for these reactions are largely determined from experimental data. The plots of assembled tubulin and the phase diagram for assembly are compared with the experimental findings and are found to agree quite well.