Steady-state spectra of tubulin and microtubules. (A) Absorbance
spectra of free tubulin (teal) and free AMCA (purple) in solution.
Intensity normalized fluorescence spectra of (B), free DL tryptophan
in solution showing highest fluorescence emission at excitation wavelengths
between 270 and 300 nm. (C) Unpolymerized GTP-tubulin, (D) microtubules
polymerized using GTP-tubulin, (E) free AMCA, and (F) microtubules
polymerized using AMCA-labeled GTP-tubulin. An energy transfer peak
not observed in Figure 1A,B (at excitation 280–300 nm, and emission at 420–450
nm) is clearly visible. Colors represent photoluminescence intensity.