Tubulin pools in differentiating neuroblastoma cells

Abstract

The distribution of tubulin in soluble, reversibly stabilized (assembled) and insoluble forms has been determined in neuroblastoma cells undergoing microtubule-dependent neurite elongation. Procedures were developed to obtain reproducible tubulin fractions and to assay total tubulin. Radioimmunoassays showed that both differentiated and nondifferentiated cells contained ~ 4pg of tubulin per cell, of which 3-10% was in an insoluble, particulate form. The amount of tubulin assembled in differentiated cells was four to five times greater than in nondifferentiated cells, constituting 48-63% and 11-16% of the total tubulin pool in the respective cell types. Calculation of the concentration of soluble tubulin in differentiated cells (~ 0.8 mg/ml) and nondifferentiated cells (~ 1.6 mg/ml) indicates that a critical concentration of subunits probably does not limit the induction of microtubule formation during neurite elongation.