T and B lymphocytes express distinct tyrosine protein kinases

Murine B and T lymphocytes each contain a protein kinase activity that catalyzes the phosphorylation of both endogenous and exogenous substrates on tyrosine residues. In B lymphocytes, endogenous substrates of 56,000 and 60,000 daltons are found in the particulate fraction. Peptide mapping experiments indicate that these two substrates are closely related but are distinct from the major 58,000-dalton tyrosine protein kinase substrate found in T lymphocytes. To determine if the same kinase is active in both B and T lymphocytes, their substrate specificities were compared using two exogenously added substrates: angiotensin I and the cytoplasmic domain of the erythrocyte band 3 protein. LSTRA, a lymphoma cell line that expresses elevated levels of the T lymphocyte kinase (Casnellie, J.E., Harrison, M.L., Hellstrom, K.E., and Krebs, E.G. (1983) J. Biol. Chem. 258, 10738-10742), was used as a source of this enzyme. Kinetic analyses indicate that angiotensin I serves as a better substrate for the LSTRA kinase than for the B cell enzyme. Band 3, however, is preferentially phosphorylated by the B cell kinase. These results indicate that B and T lymphocytes express distinct tyrosine protein kinases.