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3 Acta Biochimica Polonica

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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.

Acta Biochimica Polonica

2003

tom 50

nr 2

555-566

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 × 10-6 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.

Non-random distribution of GATC sequences in regions of promoters stimulated by the SeqA protein of Escherichia coli.

100%

Strzelczyk B. , Słomińska-Wojewódzka M. , Węgrzyn G. , Węgrzyn A.

Acta Biochimica Polonica

2003

tom 50

nr 4

941-945

The SeqA protein of Escherichia coli is not only the main negative regulator of DNA replication initiation but also a specific transcription factor. It binds to hemimethylated GATC sequences and, with somewhat different specificity, to fully methylated GATC regions. Recently, a microarray analysis was reported, in which transcriptomes of wild-type and ΔseqA strains were compared. Although in the seqA mutant the levels of some transcripts were significantly decreased while certain transcripts were evidently more abundant relative to wild-type bacteria, no correlation between the presence of GATC motifs in promoter sequences and transcription activity was found. However, here we show that when larger DNA fragments, encompassing positions from -250 to +250 relative to the transcription start site, are analyzed, some common features of GATC distribution near the promoters activated by SeqA can be demonstrated. Nevertheless, it seems that the GATC pattern is not the only determinant of SeqA-dependence of promoter activity.

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

100%

Szalewicz A. , Strzelczyk B. , Kubicz A.

Acta Biochimica Polonica

1999

tom 46

nr 1

217-221