Zinc-stimulated microtubule assembly and evidence for zinc binding to tubulin.

1. Microtubule reassembly was studied in supernatant fluids from rat brain. Tubulin in extracts from zinc-deficient animals showed an impaired ability to repolymerize compared to extracts from controls; 10 microM zinc stimulated reassembly of tubulin in extracts from zinc-deficient animals. 2. Low zinc concentrations (250-900 microM zinc in the presence of 1 mM EGTA) stimulated reassembly of tubulin in brain extracts from control rats; similar concentrations of nickel had no effect whilst cobalt was inhibitory. In the absence of EGTA 20-40 microM zinc stimulated reassembly in brain extracts from normal rats. 3. Zinc-induced changes in reassembly were associated with changes in the free sulphydryl group content of the assembled crude microtubule protein; increased assembly was associated with a higher free sulphydryl group content, decreased assembly with a lower content. 4. 65Zn was found to bind to tubulin. This binding was partly inhibited by N-ethylmaleimide.