Fig. 7.

Summary of ion specific effects showing the range of concentrations for different ions below which taxol-stabilized microtubules are stable (end of colored arrows correspond to the last SAXS profile showing the MT form factor), and, ion concentrations (indicated by colored lines after colored arrows), beyond which taxol stabilized MTs have depolymerized. The beginning and end of the colored lines correspond to ion concentrations at which SAXS profiles show MT form factor scattering and enhanced SAXS indicative of MT depolymerization, respectively. The observed trend is that the ion concentration at which MT depolymerization sets in decreases with increasing atomic number (although finer data points are needed to distinguish between Co²⁺ and Mn²⁺). The y-axis shows that the MT inner radius (obtained by fitting the form factor peaks in Figs. 5 and 6 to a hollow cylinder with fixed wall thickness of 4.9 nm) does not change in the presence of all ions studied consistent with MTs with 13 protofilaments.