Zinc binding to tubulin.

1. Zinc binding to tubulin was studied by incubating microtubules with 65Zn and measuring the 65Zn retained with tubulin on DEAE Sephadex. 2. Data showed two classes of binding site, one of very low affinity and a second class binding 0.86 g-atoms Zn/mol tubulin with a dissociation constant of approx. 110 microM. 3. Binding of zinc to the higher affinity site was 50% inhibited by 2 mM N-ethyl maleimide.