Rat Brain Tubulin: Subunit Heterogeneity and Phosphorylation

Evidence for multiple forms of the α and β subunits of tubulin isolated from rat brain has been obtained by means of SDS polyacrylamide gel electrophoresis, isoelectric focusing, and SDS hydroxylapatite column chromatography. Fourteen distinct bands, localized near pH 5.4, were formed when tubulin was subjected to isoelectric focusing in a gradient established with a very narrow range ampholyte mixture. Three tubulin subunits, a 1 ., α 2 , and β, were separated by sodium dodecyl sulfate polyacrylamide slab gel electrophoresis in a second dimension. The β subunit was more acidic than the α subunits. Brain sections were incubated in tissue culture medium containing 32 P 1 and radiolabeled tubulin was subsequently isolated and subjected to electrophoresis. Only the β subunit was labeled. All radioactivity was associated with two or three adjacent bands on isoelectric focusing gels.