RAT-BRAIN TUBULIN - SUBUNIT HETEROGENEITY AND PHOSPHORYLATION

Evidence for multiple forms of the .alpha. and .beta. subunits of tubulin isolated from rat brain was obtained by means of SDS [sodium dodecyl sulfate] 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, .alpha.1, .alpha.2 and .beta., were separated by SDS polyacrylamide slab gel electrophoresis in a 2nd dimension. The .beta. subunit was more acidic than the .alpha. subunits. Brain sections were incubated in tissue culture medium containing 32Pi and radiolabeled tubulin was subsequently isolated and subjected to electrophoresis. Only the .beta. subunit was labeled. All radioactivity was associated with 2 or 3 adjacent bands on isoelectric focusing gels.