Fig. 6.

Tubulin digestion. (a) Calculated Q_bare per dimer from sequence data. At pH 6.9, the calculated Q_bare is −47 e per dimer. (Inset) Cross-section dimensions of a microtubule constructed from an axial projection of the microtubule electron-density map (20). The 13 protofilaments are displayed as half-ellipsoids of 4.6 nm width and 3.0 nm height, around a 1.1-nm-thick cylinder of inner radius of 8.4 nm. (b) Denaturing SDS/PAGE of digested microtubules. “Control” shows untreated centrifuged microtubules in a single band. The subsequent lanes show the results for subtilisin-treated microtubules for different digestion times, obtained after centrifugation. Subtilisin is present at the 25-kDa band before centrifugation (first three lanes). (c) Amplitude of measured v_x(θ) and v_y(θ) of digested microtubules as function of E. “Control” is from Fig. 3c for undigested microtubules. (d) Offset of measured v_y(θ) of digested microtubules for different Es.