Detection of tyrosine-specific protein kinases with gastrin as exogenous substrate

Gastrin was recently shown to be phosphorylated on its single tyrosine by the epidermal growth factor (EGF)-stimulated tyrosine protein kinase (TPK). The TPK previously detected in the murine lymphoma (LSTRA) induced by the Moloney murine leukemia virus phosphorylates gastrin, the apparent Km is 65 microM and the maximum rate 1900 pmol/min per mg; the kinase is more efficient with MnCl2 than with MgCl2, is stimulated by NaVO3 and inhibited by ZnCl2. Gastrin phosphorylation is observed only when a TPK is expressed by the cell: extracts of fibroblasts infected with a temperature-sensitive mutant of the Rous sarcoma virus had no gastrin kinase activity when grown at the non-permissive temperature whereas cells grown at the permissive temperature were transformed and disclosed a clear gastrin kinase activity. Gastrin kinases were detected in various transformed cells: human lymphomas, K562 cells, cells from a patient with acute proliferative leukemia, and normal cells: human T and B lymphocytes.