FIGURE 6.
A, GTP-tubulin titration (4 μm) with various concentrations of TN-16 by differential light absorption. In this experiment, we found one binding site with an affinity constant Ka = (5 ± 2) 105 m−1. B, quenching of tubulin tryptophan fluorescence by TN-16. From these individual experiments, we determined affinity constant values (1.68 ± 0.04) 105 m−1 and (1.44 ± 0.06) 105 m−1 with GTP-tubulin (●) and GDP-tubulin (○), respectively. The difference to A may be ascribed to the different method.