Enzymes transducing extracellular signals in acute myeloid human leukemias.

The ectoenzymes gamma-glutamyltransferase (gamma-GT) and the PIP2 phospholipid phospholipase-C (PLC), a second messenger generating enzyme active on the cytoplasmic membrane bilayer, were biochemically investigated in leukemic cells isolated from 67 patients with acute leukemia. Six groups were distinguished on the basis of morphology, cytochemistry and immunophenotyping according to the FAB classification: M0, M1-M2, M3, M4, M5 and CML blast crisis (CML-BC). The activity of PLC ranged from 0.6 to 14.5 nmol/min/mg without a significant difference among groups, whereas the gamma-GT activity varied significantly from 0 to 31.6 nmol/min/mg. The highest mean activity was measured in monoblastic leukemia (M5), followed by groups M4, CML-BC and M0 (undifferentiated) while the lowest activity was found in M1-M2 and M3 groups. Within each group, activity distribution profiles of both enzymes never correlated with each other, suggesting that in leukemic cells functional-structural constituents of both membrane leaflets were independently affected by the neoplastic process.