Isolation and characterization of actin and myosin from B-lymphocytic guinea pig leukemia cells

Actin and myosin have been isolated from a guinea pig B cell leukemia line, L2C. The m.w. and amino acid compositions of these proteins are similar to actin and myosin from other nonmuscle cell types. L2C actin polymerizes to form filaments and activates the ATPase activity of skeletal muscle myosin. Actin in crude lymphocyte extracts does not polymerize as well as predicted from the critical concentration of purified lymphocyte actin suggesting that other factors in lymphocyte extracts regulate actin polymerization. Lymphocyte myosin polymerizes to form synthetic filaments at low ionic strength. Lymphocyte myosin binds to actin, but its ATPase activity is not activated by actin. Possible mechanisms for regulation of the lymphocyte contractile apparatus and its importance in a number of lymphocyte functions are discussed.