The binding of vinblastine to tubulin and to particulate fractions of mammalian brain.

Abstract

The binding of tritium-labeled vinblastine (VLB) to tubulin derived from mammalian brain was measured by Sephadex gel column chromatography and by adsorption onto diethylaminoethyl-cellulose filter paper. Tubulin purified by the reassembly method gave results consistent with prior data, obtained from ammonium sulfate-diethylaminoethyl-cellulose-purified tubulin, with a Ka for VLB of 5.2 × 106 liters/mole, and for colchicine of 2.0 × 106 liters/mole. The ratio of VLB to colchicine binding was 1:2, indicating that 1 mole of VLB binds to 240,000 daltons. Crude tubulin solutions had essentially the same binding properties as the purified protein. Binding of VLB to the microsomal-synaptosomal fraction of homogenized brain was found to be significant, and quantitatively greater than binding to the soluble tubulin fraction. The ratio of bound VLB to colchicine in the microsomal-synaptosomal fraction was 2:1. It is felt that binding of the Vinca alkaloids to tubulin and tubulin-like proteins is the primary mode of action of these drugs, and a scheme relating the observed interactions of VLB with tubulin is presented.