Human lymphocyte tubulin. Purification and characterization in normal and leukemic cells.

Tubulin has been purified from human blood and tonsil lymphocytes. Using gel filtration, the molecular weight of human lymphocyte tubulin was estimated to be 119000. The protein was shown to consist of two subunits, with molecular weights of 61000 and 58000 comparable to the alpha and beta polypeptides of human brain tubulin. A partial identity reaction was observed between lymphocyte tubulin and human tubulin when tested by double immunodiffusion against a rabbit anti-human brain tubulin antibody. In the presence of GTP, the purified protein polymerized to form microtubules. Tubulin was localized to the cell's juxtacentriolar region by immunofluorescence and electron microscopy. When assayed by a colchicine-binding assay corrected for time decay, the binding affinity was 1.50 +/- 0.86 . 10(6) M-1 and a level in normal lymphocytes of 1.21 . 10(2) +/- 0.79 g/g of soluble protein was determined. Since chronic lymphocytic leukemia lymphocytes have an anomalous capping behavior as well as an unusual susceptibility to colchicine toxicity, the properties and levels of tubulin were determined in these cells. Similar values were obtained for the level, decay rate, molecular weight, and Ka for colchicine as for normal lymphocytes. Chronic lymphocytic leukemia lymphocytes tubulin polymerized in a normal fashion. It thus appears that a decrease in the quantity for function of tubulin does not account for these anomalies in the chronic lymphocytic leukemia lymphocyte.