The Study of Tubulin-Colchicine Interactions Using Fluorescence Techniques
Colchicine is a very potent antimitotic drug, through its direct interaction with the protein tubulin. Tubulin is the building block of microtubules. These hollow fibers form the spindle figure, responsible for the transport of chromosomes during cell division. The tubulin-colchicine complex is unable to form the correct structures. Colchicine is a tricyclic component, containing trimethoxybenzene, and two seven rings, the external one of which is tropolone. It is extremely weakly fluorescent in aqueous or organic solutions. Upon binding to tubulin fluorescence appears with a maximum around 400 nm (Bhattacharyya and Wolff, 1974). Fluorescence is also induced when the molecule is immobilized by freezing (Leterrier and Rieger, 1975) or in very viscous solutions at room temperature (Bhattacharyya and Wolff, 1984). We also observed fluorescence when colchicine was dried on a glass substrate. The low quantum yield is therefore probably due to the possibilities of radiationless deactivation coupled to intramolecular flexibility. A fluorescence lifetime of 1.14 (± 0.02) ns was determined with phase fluorimetry for the tubulin-colchicine complex (Ide and Engelborghs, 1981). The binding is almost irreversible, suggesting the burial of the molecule into a deep cleft on the protein. Iodide was therefore used to estimate the exposure of the molecule. It was found to expel colchicine from its complex. Other chaotropic anions behaved in the similar way (Ide and Engelborghs, 1981).
KeywordsHuman Serum Albumin Hollow Fiber Fluorescence Lifetime Viscous Solution Correct Structure
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