Purification and characterization of the major species of tyrosine protein kinase in rat liver.

The major species of tyrosine protein kinase of rat liver, has been purified to near homogeneity from liver cytosol. When the kinase was incubated with MnCl2 and [gamma-32P]ATP, two phosphoproteins with molecular masses of 72 and 75 kilodaltons were observed. The purified kinase, called p75 kinase, phosphorylates [Val5]angiotensin II, casein, vinculin, and a 34-kilodalton protein isolated from chicken embryo fibroblasts. However, it does not phosphorylate histones or IgG from Rous sarcoma virus tumor-bearing rabbits. The kinase does not contain any of the major antigenic determinants found in retroviral tyrosine protein kinases or in epidermal growth factor-receptor kinase. p75 kinase activity, as well as viral tyrosine protein kinase activity, is stimulated by heparin. Phosphorylation of angiotensin is also stimulated by high ionic strength. In contrast, casein phosphorylation by the kinase appeared to be inhibited by high salt. Kinetic properties of p75 kinase have been determined and have revealed some striking differences from those of most other tyrosine protein kinases. For instance, p75 kinase exhibits rather stringent dependence for its activity on ATP as phosphoryl donor and Mn2+ as divalent cation.