Tyrosine phosphatase activity measurements. (A) Raft and nonraft fractions from treated and control cells were subject to tyrosine phosphatase activity measurements based on the malachite green assay using 2 different tyrosine phosphorylated peptides, TRDIpYETDYYRK and DADEpYLIPQQG. Significant increases in phosphatase activity were seen in the raft fractions for both these peptides. (B) Furthermore, to determine how much of this activity was contributed by CD45, we used an inhibitor to CD45 (Calbiochem) at a concentration of 5 μM and show that approximately 17% of the total tyrosine activity in the raft fraction is contributed by CD45.