Microtubules protofilament numbers

The binding of taxanes has been well characterized [10, 22] and shows a series of consecutive reactions involving a first fast bimolecular step (k+1 and k, ), a second slow monomolecular step (k+2, k 2) and a third step which is the structural change involving the change in the number of microtubule protofilaments. It can be proved numerically that the first bimolecular fast step of binding is diffusion controlled, thus indicating that taxanes can not directly bind to the lumenal site [22],... 

Electron microscopy (EM) has played a central role in many aspects of research on microtubules and their main protein component, tubulin. MTs were first identified in electron micrographs of plant material [1], Characteristics of the basic structural aspects of MTs were also determined by EM, revealing that MTs are hollow tubes composed of protofilaments (pf). There are most often 13 pfs, but this number can vary at least from 9 to 16. Subsequent work showed that the pfs are composed of aP-tubulin dimers arranged head-to-tail. 

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