Dissociation Constant of Tetrahymena Tubulin-Colchicine Complex

Abstract

Tetrahymena tubulin has a very low affinity for colchicine. The dissociation rate constant (k₋₁) and association rate constant(k₊₁) of Tetrahymena tubulin for colchicine were determined in comparison with those of porcine brain tubulin. The k₊₁ value of Tetrahymena tubulin was about one-twentieth that of porcine brain tubulin, and k₋₁ of Tetrahymena tubulin was about 680 times greater than that of brain tubulin. The dissociation constant(k₋₁/k₊₁) of Tetrahymena tubulin (2.7×10⁻³) turned out to be ten thousand times greater than that of brain tubulin. This large K_d value explains well the high colchicine concentration requirement reported to block cell division or cilia regeneration of this protozoan.