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The 35 kDa acid phosphatase isolated from lupin (Lupinus luteus) cotyledons displaying characteristics of LMW tartrate resistant acid phosphatases (TRAP)

100%

Szalewicz A. , Rzodeczko H. , Dudek P. , Watorek W.

nr Supplement 4

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

100%

Szalewicz A. , Strzelczyk B. , Sopel M. , Kubicz A.

nr 2

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 32P-phosphorylase a under conditions standard for the enzymes of PPP family. Proteins containing P-Ser: rabbit 32P-phosphorylase a 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). Km value for the hirudin fragment (7.55 ± 1.59 10–6M) 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.

Modulatory effect of divalent metal cations on the phosphotyrosine activity of the frog liver acid phosphatase

100%

Szalewicz A. , Strzelczyk B. , Kubicz A.

nr 1

Frog liver acid phosphatase hydrolyzes phosphotyrosine at acidic pH optimum. Mn2+, Ca2+ and Mg2+ (but not Zn2+) ions modulate this activity by shifting its pH optimum to physiological pH. This effect is not observed when p-nitrophenylphos-phate is used as a substrate. Phosphoserine and phosphothreonine are not hydrolyzed under the same conditions.

Drobnoustroje w biologicznej ochronie roślin przed chorobami grzybowymi

75%

Grzegorczyk M. , Szalewicz A. , Zarowska B. , Polomska X. , Watorek W. , Wojtatowicz M.

nr 2