The phosphatase activity of SH2-containing protein tyrosine phosphatas
e (SHP) is inhibited by its SH2 domains and C-terminal tail. In order
to determine the inhibitory effects of the SH2 domains and C-terminal
tail, we have expressed and purified the catalytic domains of SHP-1 an
d SHP-2, and the SH2 domain truncated SH P-l and SHP-2. We have then m
easured their kinetic parameters using p-nitrophenyl phosphate (p-NPP)
and phosphotyrosine (pY) as substrates under the same experimental co
nditions. The results indicate that the pH-dependent profiles of SHP-1
and SHP-2 are mainly determined by their catalytic domains. Both enzy
mes have maximum activity at pH 5.0. In addition, the phosphatase acti
vity of different forms of SHP-1 and SHP-2 decreases as the salt conce
ntration increases. Without SH2 domains, both SHP-1 and SHP-2 are no l
onger inhibited by their C-terminal tails. However, the C-terminal tai
l of SHP-1 can further prevent the salt inhibition of the phosphatase
activity. Under the same experimental conditions, the catalytic domain
of SHP-1 is two times more active than the catalytic domain of SHP-2.
). Cell. Biochem. 72:145-150, 1999. (C) 1999 Wiley-Liss, Inc.