Interaction of tubulin with non-denaturing amphiphiles.

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Abstract
Soluble purified calf brain tubulin contains extensive and easily accessible regions capable of hydrophobic interactions. The binding of non‐ionic and mild anionic detergents to this protein has been characterized by difference absorption spectroscopy and equilibrium gel chromatography with labelled ligands. Tubulin bound reversibly and co‐operatively 0.42 +/‐ 0.05 g deoxycholate per g protein and bound octyl glucoside at a minimal stoichiometry of 0.26 g per g protein. Binding of deoxycholate and octyl glucoside perturbed the protein absorption, quenched the fluorescence, and produced a moderate change in the far u.v. circular dichroism of tubulin. These changes have been interpreted as the result of detergent binding near aromatic amino acids and the production of a structural change different from detergent‐induced denaturation. Deoxycholate and octyl glucoside inhibited colchicine binding. Octyl glucoside and Triton X‐100 inhibited the in vitro self‐assembly of tubulin into microtubules, whereas small concentrations of deoxycholate were found to enhance microtubule formation.