Tubulin is phosphorylated at tyrosine by pp60 c-src in nerve growth cone membranes

Abstract. We show here that tubulin is the major in vivo substrate of the tyrosine-specific protein kinase pp60 ~- ~ in nerve growth cone membranes. Phosphotyrosine antibodies were used to demonstrate phosphotyrosyl residues in a subpopulation of ~- and ~-tubulin that was highly enriched in a subcellular fraction of growth cone membranes from fetal rat brain. The presence of phosphotyrosine-modified isoforms of a- and ~-tubulin in vivo was confirmed by 32p labeling of rat cortical neurons in culture. Tubulin in growth cone membranes was phosphorylated at tyrosine in endogenous membrane phosphorylation reactions (0.068 mol phosphotyrosine/mol a-tubulin and 0.045 tool phosphotyrosine/mol/~-tubulin), and phosphorylation was specifically inhibited by antibodie