The 35 kDa acid metallophosphatase of the frog Rana esculenta liver: studies on its cellular localization and protein phosphatase activity.

Abstract

The cellular localization of the 35 kDa, low molecular mass acid metallophosphatase (LMW AcPase) from the frog (Rana esculenta) liver and its activity towards P-Ser and P-Tyr phosphorylated peptides were studied. This enzyme was localized to the cytoplasm of hepatocytes but did not appear in other cells of liver tissue (endothelium, macrophages, blood cells). This LMW AcPase does not display activity towards (32)P-phosphorylase a under conditions standard for the enzymes of PPP family. Proteins containing P-Ser: rabbit (32)P-phosphorylasea and phosvitin are hydrolysed only at acidic pH and are poor substrates for this enzyme. The frog AcPase is not inhibited by okadaic acid and F(-) ions, the Ser/Thr protein phosphatase inhibitors. Moreover, the frog enzyme does not cross-react with specific antisera directed against N-terminal fragment of human PP2A and C-terminal conserved fragment of the eukaryotic PP2A catalytic subunits. These results exclude LMW AcPase from belonging to Ser/Thr protein phosphatases: PP1c or PP2Ac. In addition to P-Tyr, this enzyme hydrolyses efficiently at acidic pH P-Tyr phosphorylated peptides (hirudin and gastrin fragments). K(m) value for the hirudin fragment (7.55 +/- 1.59 x 10(-6) M) is 2-3 orders of magnitude lower in comparison with other substrates tested. The enzyme is inhibited competitively by typical inhibitors of protein tyrosine phosphatases (PTPases): sodium orthovanadate, molybdate and tungstate. These results may suggest that the LMW AcPase of frog liver can act as PTPase in vivo. A different cellular localization and different response to inhibition by tetrahedral oxyanions (molybdate, vanadate and tungstate) provide further evidence that LMW AcPase of frog liver is distinct from the mammalian tartrate-resistant acid phosphatases.

Expression, purification, and characterization of a novel acid phosphatase that displays protein tyrosine phosphatases activity from Metarhizium anisopliae strain CQMa102

“…So based on the purified phosphatase's most suitable pH, substrate specificity, specific inhibitors and conservative sequence of amino acids, we identified the purified phosphatase as an acid phosphatase that displays protein tyrosine phosphatase activity. Some acid phosphatase have been reported to have protein tyrosine phosphatase activity, 7,34,35) they appear to be cytoplasmic in origin, have acidic pH preference, and generally accept pNPP as substrate. 28) Like other acid phosphatase containing protein tyrosine phosphatase activity reported, [34][35][36] the purified phosphatase from M.anisopliae displayed higher activity for pNPP than for phosphotyrosine residues compared with classical PTPase.…”

“…Some acid phosphatase have been reported to have protein tyrosine phosphatase activity, 7,34,35) they appear to be cytoplasmic in origin, have acidic pH preference, and generally accept pNPP as substrate. 28) Like other acid phosphatase containing protein tyrosine phosphatase activity reported, [34][35][36] the purified phosphatase from M.anisopliae displayed higher activity for pNPP than for phosphotyrosine residues compared with classical PTPase. Additionally, NaF is more characteristic of an inhibitor of protein Ser/Thr phosphatases than of protein tyrosine phosphatase, several acid phosphatases containing protein tyrosine phosphatase activity are reported to be inhibited by NaF, 37,38) it was the same that NaF exhibited inhibition in our experiments .…”