Purification and Characterization of Actin from Normal and Chronic Lymphocytic Leukemia Lymphocytes1

Previous studies from this laboratory have shown actin to be a major protein of human lymphocytes (Stark, R., Liebes, L. F., Nevrla, D., and Silber, R. Biochem. Med., 27: 200-206, 1982). We now report the purification to homogeneity and characteri zation of actin from blood lymphocytes of normal subjects and patients with chronic lymphocytic leukemia. The recovery of the purified protein was about 20%. The properties of the lympho cyte actins were compared to each other and to those of rabbit skeletal muscle actin. Lymphocyte actin consisted of ßand 7 forms in a 2:1 ratio. The M, 42,000 was determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Normal and leukemic lymphocyte actin had similar polymerization properties as assessed by viscosity measurements at 25°and 4°,and the ultrastructural appearance of the filaments was the same. Similar patterns were observed between normal and chronic lympho cytic leukemia actin tryptic digests analyzed by high-performance liquid chromatography. The V,™» of the actin-activated myosin Mg2+ ATPase activity was compared using rabbit skeletal muscle heavy meromyosin and subfragment 1 preparations. The values obtained with rabbit skeletal muscle and normal lymphocyte actin were identical. The Vmax observed with chronic lymphocytic leukemia lymphocyte actin was 70% of that obtained with normal lymphocyte actin. The amount of actin needed to produce halfmaximal activation (Klarem) of heavy meromyosin and subfrag ment 1 were, respectively, 26 and 25 ^M for normal lymphocytes and 18 and 24 /¿Mfor chronic lymphocytic leukemia lymphocytes. The anomalous ATP activation by actin did not reflect differences in B-:T-cell subpopulations between chronic lymphocytic leuke mia and normal lymphocytes. The possible significance of the observed differences between the myosin Mg2+ ATPase activa tion by chronic lymphocytic leukemia and normal lymphocyte actin is discussed.