DECREASE IN THE PHOSPHOTYROSINE PHOSPHATASE-ACTIVITY IN THE PLASMA-MEMBRANE OF HUMAN NEUTROPHILS ON STIMULATION BY PHORBOL 12-MYRISTATE 13-ACETATE

Phorbol 12-myristate 13-acetate (PMA) induced a decrease in the phosph otyrosine phosphatase (PTPase) activity in human neutrophils. The decr ease in the activity induced by PMA was blocked by the treatment of th e cells with staurosporine, indicating that protein kinase C is involv ed in the decrease. The PTPase activity was localized in the plasma me mbrane. The activity in the membrane with the optimum pH at 5.5 had a K-m value for phosphotyrosine of 2.2 mM and V-max of 2.0 mu mol/min pe r mg of protein. No activity was observed against phosphoserine and ph osphothreonine. Vanadate, molybdate, zinc and a sulfhydryl reagent, p- chloromercuribenzenesulphonic acid, inhibited the PTPase. The PMA-indu ced decrease in activity was almost completely recovered by treatment of the plasma membrane with Triton X-100 at low concentrations which d id not solubilize the activity from the membrane. When the plasma memb rane was treated with trypsin, the PTPase of the membrane from PMA-tre ated cells was mostly protected from the proteinase attack while that from the resting cells was not protected. Pretreatment of the plasma m embrane with Triton X-100 enabled trypsin to gain access to all the PT Pase in the membrane from both PMA-treated and resting cells. The PMA treatment affected neither subcellular localization of the PTPase nor the orientation of the plasma membrane vesicles. These findings sugges t that conformational changes of the enzyme induced by PMA result in t he decrease in PTPase activity.