Figure 8. Reduction of intrinsic tryptophan of tubulin by cembrenoids and determination of dissociation constant.

(A) The effects of cembrenoids on the tryptophan fluorescence spectra of tubulin are shown. Spectra are monitored in the absence (Ct) and presence of 5 µM of Cembrene, Incensole oxide, Colchicine or Paclitaxel (B) The change in the fluorescence intensity of tubulin (ΔF) is plotted against concentrations of each compound. The dissociation constant (Kd) for Cembrene, Incensole oxide, Colchicine and Paclitaxel binding to tubulin is estimated using an equation described in the methods. Data are represented as the mean ± MAD of two independent experiments.