In mammalian brain, β-tubulin occurs as a mixture of four isotypes designated as types I, II, III, and IV. It has been speculated in recent years that the different tubulin isotypes may confer functional diversity to microtubules. In an effort to investigate whether different tubulin isotypes differ in their functional properties we have studied the colchicine binding kinetics of bovine brain tubulin upon removal of the β(III) isotype. We found that the removal of the β(III) isotype alters the binding kinetics from biphasic to monophasic with the disappearance of the slow phase. The kinetics become biphasic with the reappearance of the slow phase when the β(III)-depleted tubulin was mixed with the β(III) fraction eluted from the affinity column with 0.5 M NaCl. The analysis of the kinetic data reveals that the tubulin dimers containing β(III) bind colchicine at an on-rate constant of 35 M-1 s-1 while those lacking β(III) bind at 182 M-1 s-1. Our results strongly suggest that the β-subunit plays a very important role in the interaction of tubulin with colchicine.
|Original language||English (US)|
|Number of pages||3|
|Journal||Journal of Biological Chemistry|
|State||Published - Mar 1 1991|
ASJC Scopus subject areas
- Molecular Biology
- Cell Biology