TABLE 3.
Effect of solvent variables in the tubulin dimer dissociation constant and the critical concentration for polymerization
| Condition | Dimer dissociation constanta |
Critical concentrationb |
||
|---|---|---|---|---|
| Kd, nM | Observed/control | CC, μm | Observed/control | |
| PM buffer | 96 (84–107) | 1.0 | NDc | ND |
| +GDP 0.5 mm | 76 (71–81) | 0.8 | >10 | >2 |
| +GTP 0.5 mm | 76 (69–83) | 0.8 | 4.7 (±0.3) | 1.0 |
| + Urea 0.3 m | 115 (101–131) | 1.2 | 9.2 (±1.2) | 2.0 |
| + TMAO 0.3 m | 93 (84–103) | 1.0 | 1.5 (±0.4) | 0.3 |
| +NaCl 0.5 m | 51 (48–54) | 0.5 | 6.5 (±0.9) | 1.4 |
a The values of Kd were determined using the fluorescence anisotropy assay. The experiment in PM buffer was the control condition. Values reported are the best-fit with 68% confidence intervals in parentheses. The anisotropy of the monomer species was fixed for these analyses.
b The values of CC were measured employing the pelleting assay. The experiment in presence of 0.5 mm GTP was considered as the control condition. Values in parentheses are the standard deviations of replicate experiments.
c ND indicates not determined.