The 18 kDa cytosolic acid phosphatase from bovine live has phosphotyrosine phosphatase activity on the autophosphorylated epidermal growth factor receptor.
In this paper we demonstrate that the cytosolic low-Mr acid phosphatase purified from bovine liver has phosphotyrosine protein phosphatase activity on 32P-autophosphorylated epidermal growth factor (EGF) receptor. This activity was significantly inhibited by orthovanadate and p-hydroxymercuribenzoate; the latter result indicates that free sulfhydryl groups are required for phosphotyrosine phosphatase activity. The enzyme was active in a broad pH range, with maximum activity between pH 5.5 and 7.5. The apparent Km for 32P-EGF receptor dephosphorylation was 4 nM. The enzyme appeared to be specific for phosphotyrosine in that it dephosphorylated the autophosphorylated EGF receptor and L-phosphotyrosine, but not 32P-Ser-casein, L-phosphoserine or L-phosphothreonine. These data suggest that the cytosolic low-Mr acid phosphatase might play a regulatory role in EGF receptor-dependent transmembrane signalling.
Ramponi
G
G
Department of Biochemical Sciences, University of Firenze, Italy.
Manao
G
G
Camici
G
G
Cappugi
G
G
Ruggiero
M
M
Bottaro
D P
DP
D000135:Acid Phosphatase / Q000378:metabolism*; D000818:Animals; D002417:Cattle; D003600:Cytosol / Q000201:enzymology; D004591:Electrophoresis, Polyacrylamide Gel; D004815:Epidermal Growth Factor / Q000378:metabolism*; D066246:ErbB Receptors / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D008099:Liver / Q000201:enzymology*; D010766:Phosphorylation; D013379:Substrate Specificity
D004815:Epidermal Growth Factor; D066246:ErbB Receptors; D000135:Acid Phosphatase