| We present data that SHP 1 and PTPH 1 are present in highly enriched protein fractions that exhibit PTPase activities toward a tyrosine phosphorylated TCR zeta substrate ( specific activity ranging from 0 . 23 to 40 pmol / min / microg ) . ^^^ Subsequent transfection assays indicated that SHP 1 and PTPH 1 are the two principal PTPases capable of regulating the phosphorylation state of the TCR zeta ITAMs , with PTPH 1 directly dephosphorylating zeta . ^^^ This is the first reported demonstration that PTPH 1 is a candidate PTPase capable of interacting with and dephosphorylating TCR zeta . . ^^^ |