Sm. Bradykalnay et Nk. Tonks, PURIFICATION AND CHARACTERIZATION OF THE HUMAN PROTEIN-TYROSINE-PHOSPHATASE, PTP-MU, FROM A BACULOVIRUS EXPRESSION SYSTEM, Molecular and cellular biochemistry, 128, 1993, pp. 131-141
The receptor like PTPase, PTP mu, displays structural similarity in it
s extracellular segment to members of the immunoglobulin superfamily o
f cell adhesion molecules. The full length form of PTP mu (200 kD) and
a construct expressing only the intracellular PTPase domain-containin
g segment (80 kD) were expressed in the baculovirus/Sf9 cell system, p
urified and characterized. Full length PTP mu was membrane associated
while the truncated form was recovered in the soluble fraction. PTP mu
preferentially dephosphorylated a reduced carboxamidomethylated and m
aleylated derivative of lysozyme (RCML) over other tyrosine phosphoryl
ated substrates such as myelin basic protein (MBP) or the synthetic pe
ptide EDNDYINASL. The enzymatic properties of the soluble, truncated f
orm of the enzyme were examined in detail. The pH optimum was 7.5. It
dephosphorylated RCML with a K-m of 400 nM and a V-max of 725 nmol/min
/mg. This form of the enzyme was 2 fold more active than full length P
TP mu. Trypsinization of the full length form inhibited activity. Vana
date and molybdate, potent tyrosine phosphatase inhibitors, abolished
activity of the enzyme. Zn++ and Mn++ ions, polylysine, poly-glu/tyr,
and spermine were also inhibitory.