We have been interested in the role of tyrosine protein kinases in the regulation of normal cellular metabolism. To examine this question, we have concentrated on hematopoietic cells as model systems. We have initiated studies on both the cellular and molecular level to identify and characterize the tyrosine protein kinase activities present in lymphocytes and macrophages. As compared to most normal cells and tissues, these cells express relatively high levels of protein kinases that phosphorylate endogenous protein substrates on tyrosine residues. For example, normal T lymphocytes as well as almost all T lymphoma-derived cell lines tested to date possess a predominant substrate of M?r? 58,000 (p58). The phosphorylation of p58 is thought to represent an autophosphorylation reaction. Mouse B lymphocytes and macrophages lack p58 but do express other endogenous substrates for tyrosine protein kinase activity of M?r? 60,000 and 56,000 (B lymphocytes) or 59,000 and 56,000 (macrophages). Peptide mapping experiments indicate that T cell p58, B cell p60 and macrophage p59 are structurally distinct. The principal tyrosine protein kinase activities expressed in B and T lymphocytes can also be distinguished by their differing substrate specificities using exogenously added peptide and protein substrates. These studies indicate that T and B lymphocytes contain distinct tyrosine protein kinases. In an effort to better understand the nature of the enzymes involved, we have begun developing procedures for the isolation of a tyrosine protein kinase from calf thymus. The enzyme has been purified several hundred fold using chromatography on columns of DEAE-cellulose, hydroxylapatite, heparin-agarose and casein-agarose. The partially purified enxyme shows an unusual activation by high ionic strength and is capable of utilizing CoATP and MnATP as substrates. (LB)
Showing the most recent 10 out of 70 publications
