FIGURE 9.

Lyn from both desensitized and nondesensitized cells is activated by (p)₂ITAM binding. Lyn was immunoprecipitated from NP₇BSA desensitized (◆) and unstimulated (–□–) K46 μ cells by either anti-receptor (A) or anti-Lyn (B) immunoprecipitation. Immunoprecipitates from 10 × 10⁶ cell equivalents were exposed to varied concentrations of (p)₂ITAM for 1 h before kinase activity was assayed as described in Materials and Methods. Data are shown as fold activity plotted against the micromolar concentration of stimulating (p)₂ITAM peptide. Fold stimulation was calculated by first subtracting the background counts per minute (reaction mix minus kinase) from the counts per minute at each data point, then dividing each corrected data point value by the value of the zero peptide control. The basal kinase activity of anti-Lyn immunoprecipitates from unstimulated cells was 81,335 cpm and that from desensitized cells was 49,625 cpm with a background counts per minute of 4,500; that from anti-receptor IP of unstimulated cells was 4,241 cpm, and that from desensitized cells was 3,577 cpm with a background counts per minute of 2,000.