Tyrosine protein kinase activity in normal and leukaemic human blood cells

Tyrosine protein kinase (TPK) activity was measured in subcellular fractions of normal granulocytes, lymphocytes and monocytes, and acute and chronic myeloid and lymphoid leukaemic cells. Of several tested tyrosine-containing substrates, poly (glutamic acid: tyrosine = 4:1) (S1) proved to be the best synthetic substrate. High cytosolic TPK activity was found in every cell type. Different TPKs may exist in various cell fractions, as was indicated by the difference in Km values for S1 in cell fractions of normal granulocytes and lymphocytes. No significant difference was found in total TPK activity between normal and leukaemic cells, indicating that total TPK activity is not related to the leukaemic process itself. A highly significant difference was found in membrane fractions in normal granulocytes and M1-M2 AML cells versus normal monocytes and M4-M5 AML cells, suggesting an association between TPK activity and monocytic differentiation in these cell fractions.