Electrophoretic separation of tubulin α and β subunits after S-sulfonation

The modification of tubulin cysteine and cystine residues to S-sulfocysteines caused a distinct separation of the α and β subunits in a continuous sodium dodecyl sulfate polyacrylamide gel system. The well-separated subunit bands permitted investigation of the phosphorylation of α and β tubulin subunits. The incubation of tubulin fraction with [γ^-32P]ATP demonstrated that both subunits were phosphorylated in vitro. The incorporation of ³²PO₄ into sea urchin eggs, however, failed to cause phosphorylation of tubulin in vivo.