title: The interactions of tropolone with magnesium ions and tubulin.
abstract: Tropolone, a single analog of colchicine, interacts with Mg2 with the formation of a 1 : 1 complex and an apparent equilibrium binding constant Kb of 1.4 x 10(4) M(-1) in neutral aqueous solution at 25 degrees C. The tropolone-Mg2 complex, but not tropolone, is fluorescent. Since tubulin binds Mg2 (Frigon, R.P. and Timasheff, S.N. (1975) Biochemistry 14, 4567-4573), previous reports of tropolone interaction with tubulin in Mg2 -containing buffers must be critically re-examined. Fluorescence and difference absorption spectroscopy experiments performed at essentially constant Mg2 activity indicate that tubulin does bind tropolone, but the optical effects are too weak to use in quantitative studies.
mesh_terms: D000818:Animals; D002413:Cations, Divalent; D002417:Cattle; D003508:Cycloheptanes; D006863:Hydrogen-Ion Concentration; D008274:Magnesium; D011485:Protein Binding; D013050:Spectrometry, Fluorescence; D013057:Spectrum Analysis; D014334:Tropolone; D014404:Tubulin
chemical_list: D002413:Cations, Divalent; D003508:Cycloheptanes; D014404:Tubulin; D014334:Tropolone; D008274:Magnesium