Effect of membrane PTP on Syk activity.

The phosphorylation state of Syk ICs was analyzed by antiphosphotyrosine immunoblotting under various conditions: IC from unincubated SS cells (lane 1); IC after incubation with membrane suspensions, either with Na₃VO₄ (inhibited PTP, −) (lane 2), or in its absence (active PTP, +) (lane 3); IC after preincubation with inhibited PTP (−) or active PTP (+) followed by IC assays (lanes 4 and 5, respectively). One representative experiment is shown. Similar data were obtained in 3 other experiments with SS cells and in 2 experiments with AA cells.