Characterization of tyrosine protein kinase associated with subcellular components of human colonic epithelium.

Tyrosine protein kinase (TPK) co-isolated with subcellular components derived from human colonic epithelium. The highest TPK activity, measured in the Triton X-100-insoluble cytoskeletal pellet, was directly related to the degree of malignancy of colonic tissue. TPK activity was assayed by measuring the incorporation of [gamma-32P] from [gamma-32]ATP into the synthetic polymer [Glu80Tyr20]n substrate. Lineweaver-Burk plots yielded an apparent Km of 167 micrograms/ml for [Glu80Tyr20]n and of 19 microM for ATP: Vmax for the phosphate donor was 0.9 nmol/min/mg protein. TPK activity was markedly stimulated by the metal ions Mg2+ and Mn2+ and significantly suppressed by tyrphostins, potent specific TPK inhibitors, shown to interfere with TPK-dependent growth processes. This is first report to present evidence for TPK activity associated with cytoskeleton-enriched subcellular preparations harvested from human colonic epithelium.