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PubMed1986

The ATP, Mg-dependent phosphatase: role of Mg ions in the expression of the phosphorylase phosphatase activity.

The activation of the ATP, Mg-dependent phosphatase [FCM] by kinase FA has been shown to involve the phosphorylation or thiophosphorylation of the modulator subunit [M] and the consequent isomerization of the catalytic subunit [FC] into the active conformation. The inactive catalytic subunit [free FC] exhibits substantial activity in the presence of non-physiological concentrations of Mn ions whereas the Mn2+-activation of the intact FCM-enzyme requires the proteolytic destruction of the modulator subunit. The present study points to the importance of Mg2+ in the activation of the phosphatase. The inactive catalytic unit can be activated by millimolar concentrations of Mg2+ and the thiophosphorylated FCM-enzyme only expresses its phosphorylase phosphatase activity after a subsequent trypsin treatment in the presence of Mg ions.

Adenosine Triphosphate↗
PubMed1993

Correlation of acid phosphatase but not alkaline phosphatase activity with myelination in the developing mouse brain.

1. Neonatal mice received subcutaneous injections of buffer, thiourea (TU) or propylthiouracil (PTU). 2. The PTU-treated mice were sacrificed on postnatal day 14 (P14) and the TU-treated mice on P28. 3. Brain weights of the TU- and PTU-treated mice were not significantly different from the controls. 4. Acid but not alkaline phosphatase activity in the brainstem decreased after TU and PTU treatment. 5. Myelination as indicated by intensity of luxol fast blue staining was weaker in the drug-treated animals. 6. The level of myelin marker enzyme, 2',3'-cyclic nucleotide 3'-phosphohydrolase, was lower in the brainstem of PTU-treated animals. 7. The results suggest a correlation between acid phosphatase but not alkaline phosphatase activity with myelination in the developing mouse brain.

2',3'-Cyclic Nucleotide 3'-Phosphodiesterase↗
PubMed1990

An investigation of the substrate specificity of protein phosphatase 2C using synthetic peptide substrates; comparison with protein phosphatase 2A.

The synthetic phosphopeptide RRATpVA was found to be the most effective substrate for protein phosphatase 2C (PP2C) so far identified. Replacement of phosphothreonine by phosphoserine decreased activity over 20-fold and a striking preference for phosphothreonine was also observed with two other substrates (RRSTpTpVA and casein) that were phosphorylated on both serine and threonine. Replacement of the C-terminal valine in RRATpVA by proline abolished dephosphorylation, while exchanging the N-terminal alanine by proline had no effect. The preference for phosphothreonine and the effect of proline are similar to protein phosphatase 2A (PP2A). However, the peptide RRREEETpEEEAA, an excellent substrate for PP2A, was not dephosphorylated by PP2C, and substitution of the C-terminal valine in RRATpVA by glutamic acid reduced the rate of dephosphorylation by PP2C over 10-fold, without affecting dephosphorylation by PP2A. Addition of two extra N-terminal arginine residues to RRASpVA increased PP2A catalysed dephosphorylation 4- to 5-fold, without altering dephosphorylation by PP2C. These results represent the first study of the specificity of PP2C using synthetic peptides, and strengthen the view that this approach may lead to the development of more effective and specific substrates for the serine/threonine-specific protein phosphatases.

Alanine↗
PubMed2001

Myotonic dystrophy protein kinase phosphorylates the myosin phosphatase targeting subunit and inhibits myosin phosphatase activity.

Myotonic dystrophy protein kinase (DMPK) and Rho-kinase are related. An important function of Rho-kinase is to phosphorylate the myosin-binding subunit of myosin phosphatase (MYPT1) and inhibit phosphatase activity. Experiments were carried out to determine if DMPK could function similarly. MYPT1 was phosphorylated by DMPK. The phosphorylation site(s) was in the C-terminal part of the molecule. DMPK was not inhibited by the Rho-kinase inhibitors, Y-27632 and HA-1077. Several approaches were taken to determine that a major site of phosphorylation was T654. Phosphorylation at T654 inhibited phosphatase activity. Thus both DMPK and Rho-kinase may regulate myosin II phosphorylation.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed1987

Evolution of localization of reactions of adenosine triphosphatase (Mg++-ATP-ase), 5'nucleotidase (5'nt), alkaline phosphatase (AP), and acid phosphatase (AcP) in developing rat testis. II. After CdCl2 treatment.

The described experiments show the influence of a single dose of cadmium chloride (1.5 mg CdCl2/kg body weight applied intraperitoneally) on development of the male gonads from the 1st d of post-fetal life to 1.5 a of life. In the case of the enzymes triggering transportation processes, adenosine triphosphatase stimulated by Mg++ (Mg++-ATP-ase), alkaline phosphatase (AP), and 5'nucleotidase (5'Nt), a considerable damages begin to appear in the 15th d of life whereas in the case of acid phosphatase (AcP) already in the 1st d of life whereas in the case of acid phosphatase (AcP) already in the 1st d of life. These damages increase with age reaching their maximum in the 45th d of life.

5'-Nucleotidase↗
PubMed1993

Molecular cloning and expression of the catalytic subunit of bovine pyruvate dehydrogenase phosphatase and sequence similarity with protein phosphatase 2C.

After many unsuccessful attempts to detect cDNA encoding the catalytic subunit of bovine pyruvate dehydrogenase phosphatase (PDPc) in bovine cDNA libraries, an approach based on the polymerase chain reaction (PCR) was undertaken. Overlapping DNA fragments were generated by PCR from bovine genomic DNA and from cDNA synthesized from total RNA with synthetic oligonucleotide primers on the basis of experimentally determined amino acid sequences. The DNA fragments were subcloned and sequenced. The complete cDNA is 1900 base pairs in length and contains an open reading frame of 1614 nucleotides encoding a putative presequence of 71 amino acid residues and a mature protein of 467 residues with a calculated M(r) of 52,625. Hybridization analysis showed a single mRNA transcript of about 2.0 kilobases. Comparison of the deduced amino acid sequences of the mitochondrial PDPc and the rat cytosolic protein phosphatase 2C indicates that these protein serine/threonine phosphatases evolved from a common ancestor. The mature form of PDPc was coexpressed in Escherichia coli with the chaperonin proteins groEL and groES. The recombinant protein (rPDPc) was purified to near homogeneity. Its activity toward the bovine 32P-labeled pyruvate dehydrogenase complex was Mg(2+)-dependent and Ca(2+)-stimulated and comparable to that of native bovine PDP. An active, truncated form of rPDPc, with M(r) approximately 45,000, was produced in variable amounts during growth of cells and/or during the purification procedure.

Amino Acid Sequence↗
PubMed1987

High-affinity binding of glycogen-synthase phosphatase to glycogen particles in the liver. Role of glycogen in the inhibition of synthase phosphatase by phosphorylase a.

1. Post-mitochondrial supernatants were prepared from the livers of 24 h-fasted rats. Upon centrifugation at high speed, the major part of the glycogen-synthase phosphatase activity sedimented with the microsomal fraction. However, two approaches showed that the enzyme was associated with residual glycogen rather than with vesicles of the endoplasmic reticulum. Indeed, the activity was entirely solubilized when the remaining glycogen was degraded either by glucagon treatment in vivo or by alpha-amylolysis in vitro. No evidence could be found for an association of glycogen-synthase phosphatase with the smooth endoplasmic reticulum, as isolated with the use of discontinuous sucrose gradients. 2. After solubilization by glucagon treatment in vivo, synthase phosphatase could be transferred to glycogen particles with very high affinity. Half-maximal binding occurred at a glycogen concentration of about 0.25 mg/ml, whereas glycogen synthase and phosphorylase required 1.5-2 mg/ml. 3. In gel-filtered extracts prepared from glycogen-depleted livers, the activation of glycogen synthase was not inhibited at all by phosphorylase alpha. The inhibition was restored when the liver homogenates were prepared in a glycogen-containing buffer. The effect was half-maximal at a glycogen concentration of about 0.25 mg/ml, and virtually complete at 1 mg/ml. These findings explain long-standing observations that in fasted animals the liver contains appreciable amounts of both synthase and phosphorylase in the active form.

Animals↗
PubMed1999

The RCN1-encoded A subunit of protein phosphatase 2A increases phosphatase activity in vivo.

Protein phosphatase 2A (PP2A), a heterotrimeric serine/threonine-specific protein phosphatase, comprises a catalytic C subunit and two distinct regulatory subunits, A and B. The RCN1 gene encodes one of three A regulatory subunits in Arabidopsis thaliana. A T-DNA insertion mutation at this locus impairs root curling, seedling organ elongation and apical hypocotyl hook formation. We have used in vivo and in vitro assays to gauge the impact of the rcn1 mutation on PP2A activity in seedlings. PP2A activity is decreased in extracts from rcn1 mutant seedlings, and this decrease is not due to a reduction in catalytic subunit expression. Roots of mutant seedlings exhibit increased sensitivity to the phosphatase inhibitors okadaic acid and cantharidin in organ elongation assays. Shoots of dark-grown, but not light-grown seedlings also show increased inhibitor sensitivity. Furthermore, cantharidin treatment of wild-type seedlings mimics the rcn1 defect in root curling, root waving and hypocotyl hook formation assays. In roots of wild-type seedlings, RCN1 mRNA is expressed at high levels in root tips, and accumulates to lower levels in the pericycle and lateral root primordia. In shoots, RCN1 is expressed in the apical hook and the basal, rapidly elongating cells in etiolated hypocotyls, and in the shoot meristem and leaf primordia of light-grown seedlings. Our results show that the wild-type RCN1-encoded A subunit functions as a positive regulator of the PP2A holoenzyme, increasing activity towards substrates involved in organ elongation and differential cell elongation responses such as root curling.

Arabidopsis↗
PubMed1996

Phosphorylation of the large subunit of myosin phosphatase and inhibition of phosphatase activity.

The partially purified myosin-bound phosphatase had an associated protein kinase that phosphorylated the holoenzyme, primarily on the large (130-kDa) subunit. Phosphorylation of the 130-kDa subunit resulted in inhibition of phosphatase activity. The major site of phosphorylation was threonine 654 of the 130-kDa subunit or threonine 695 of the 133-kDa isoform. Phosphorylation of the large subunit did not dissociate the holoenzyme. Dephosphorylation of the large subunit was achieved by the holoenzyme, and addition of the catalytic subunit of the type 2A enzyme did not increase the rate of dephosphorylation. The associated kinase was inhibited by chelerythrine, with half-maximal inhibition at approximately 5 microM (in 150 microM ATP). The associated kinase phosphorylated two synthetic peptides, one corresponding to the sequence flanking the phosphorylated threonine, i.e. 648-661 of the 130-kDa subunit, and the other to a known protein kinase C substrate, i.e. a modified sequence from the autoinhibitory region of epsilon protein kinase C. The associated kinase was activated by arachidonic and oleic acid and to a lesser extent by myristic acid. The protein kinase that phosphorylated the 130-kDa subunit and resulted in inhibition of myosin phosphatase activity was not identified.

Adenosine Triphosphate↗
PubMed2001

Mutational and kinetic evaluation of conserved His-123 in dual specificity protein-tyrosine phosphatase vaccinia H1-related phosphatase: participation of Tyr-78 and Thr-73 residues in tuning the orientation of His-123.

Active-site cysteine strategically positioned in the P-loop of protein-tyrosine phosphatases has been suggested to be further stabilized by hydrogen bonding arrays radiating out from the P-loop to neighboring residues. In this work, we investigated the structural role of histidine array in HC(X)(5)RS motif of the vaccinia H1-related protein phosphatase (VHR), using site-directed mutagenesis in conjunction with an extensive kinetic analysis. Conserved His-123 was mutated along with neighboring residues Tyr-78 and Thr-73. The increased pK(a) values of active-site Cys-124 found in Y78F and T73A mutants (6.51 and 6.75, respectively) were comparable to those of H123A and H123F mutants. Kinetic evaluation of Y78F and T73A mutants further implicates that the mutations perturb the relative position of Cys-124 within the P-loop. These results imply that Tyr-78 and Thr-73 make up an essential part of the His-123 array and structurally tune the Cys-124 position. Tyr-78 of VHR turns out to be the invariant Tyr reported in several protein-tyrosine phosphatases by a structure-based sequence alignment. Therefore, orientation of the imidazole ring of His-123 by the invariant Tyr-78 is crucial for maintaining the proper position of Cys-124 in the P-loop.

Base Sequence↗
PubMed2005

The protein phosphatase 2A phosphatase activator is a novel peptidyl-prolyl cis/trans-isomerase.

The protein phosphatase 2A (PP2A) phosphatase activator (PTPA) is an essential protein involved in the regulation of PP2A and the PP2A-like enzymes. In this study we demonstrate that PTPA and its yeast homologues Ypa1 and Ypa2 can induce a conformational change in some model substrates. Using these model substrates in different assays with and without helper proteases, this isomerase activity is similar to the isomerase activity of FKBP12, the human cyclophilin A, and one of its yeast homologs Cpr7 but dissimilar to the isomerase activity of Pin1. However, neither FKBP12 nor Cpr7 can reactivate the inactive form of PP2A. Therefore, PTPA belongs to a novel peptidyl-prolyl cis/trans-isomerase (PPIase) family. The PPIase activity of PTPA correlates with its activating activity since both are stimulated by the presence of Mg2+ATP, and a PTPA mutant (Delta208-213) with 400-fold less activity in the activation reaction of PP2A also showed almost no PPIase activity. The point mutant Asp205 --> Gly (in Ypa1) identified this amino acid as essential for both activities. Moreover, PTPA dissociates the inactive form from the complex with the PP2A methylesterase. Finally, Pro190 in the catalytic subunit of PP2A (PP2AC) could be identified as the target Pro isomerized by PTPA/Mg2+ATP since among the 14 Pro residues present in 12 synthesized peptides representing the microenvironments of these prolines in PP2AC, only Pro190 could be isomerized by PTPA/Mg2+ATP. This Pro190 is present in a predicted loop structure near the catalytic center of PP2AC and, if mutated into a Phe, the phosphatase is inactive and can no longer be activated by PTPA/Mg2+ATP.

Adenosine Triphosphate↗
PubMed1988

Evaluation of Leu-M5 (CD11c) in hairy cell leukemia by the alkaline phosphatase anti-alkaline phosphatase technique.

The concomitant presence of B antigens and of the antigen recognized by the monoclonal antibody Leu-M5 (CD11c) on neoplastic lymphoid cells has been reported to be largely restricted to hairy cell leukemia (HCL). The authors studied Leu-M5 reactivity of neoplastic cells from 59 patients whose specimens were referred with a stated diagnosis of HCL by using the alkaline phosphatase anti-alkaline phosphatase technique on peripheral blood (PB) and bone marrow (BM) specimens. Tartrate-resistant acid phosphatase (AcP-T) activity was also studied. In 49 patients, HCL had been confirmed previously by BM biopsy, and specimens were evaluated for disease status during or after therapy with interferon (IFN) or 2'-deoxycoformycin. The remaining ten patients were newly referred for confirmation of the diagnosis of HCL before therapy. In all 55 patients in whom the BM biopsy demonstrated HCL, virtually every leukemic cell was Leu-M5 reactive, and the reaction proved, in some cases, to be helpful in the detection of small numbers of hairy cells in PB or BM preparations. AcP-T reactivity was demonstrated in the neoplastic cells of 52 of these 55 patients, including all but 3 of those receiving IFN, and was helpful in confirming persistent leukemia when interpretation of BM biopsy sections was difficult because the numbers of hairy cells were small. However, in four of the ten newly referred patients, BM biopsy showed features of splenic lymphoma with villous lymphocytes, rather than HCL. The neoplastic cells of these four patients were of B-cell origin and in three were Leu-M5 reactive. The authors' study indicates that Leu-M5 is present in nearly all hairy cells, but its presence in conjunction with other B-cell markers is not specific for HCL.

Acid Phosphatase↗
PubMed2000

Embryonic morphogenesis in Caenorhabditis elegans integrates the activity of LET-502 Rho-binding kinase, MEL-11 myosin phosphatase, DAF-2 insulin receptor and FEM-2 PP2c phosphatase.

let-502 rho-binding kinase and mel-11 myosin phosphatase regulate Caenorhabditis elegans embryonic morphogenesis. Genetic analysis presented here establishes the following modes of let-502 action: (i) loss of only maternal let-502 results in abnormal early cleavages, (ii) loss of both zygotic and maternal let-502 causes elongation defects, and (iii) loss of only zygotic let-502 results in sterility. The morphogenetic function of let-502 and mel-11 is apparently redundant with another pathway since elimination of these two genes resulted in progeny that underwent near-normal elongation. Triple mutant analysis indicated that unc-73 (Rho/Rac guanine exchange factor) and mlc-4 (myosin light chain) act in parallel to or downstream of let-502/mel-11. In contrast mig-2 (Rho/Rac), daf-2 (insulin receptor), and age-1 (PI3 kinase) act within the let-502/mel-11 pathway. Mutations in the sex-determination gene fem-2, which encodes a PP2c phosphatase (unrelated to the MEL-11 phosphatase), enhanced mutations of let-502 and suppressed those of mel-11. fem-2's elongation function appears to be independent of its role in sexual identity since the sex-determination genes fem-1, fem-3, tra-1, and tra-3 had no effect on mel-11 or let-502. By itself, fem-2 affects morphogenesis with low penetrance. fem-2 blocked the near-normal elongation of let-502; mel-11 indicating that fem-2 acts in a parallel elongation pathway. The action of two redundant pathways likely ensures accurate elongation of the C. elegans embryo.

Amino Acid Sequence↗
PubMed1998

A specific alkaline phosphatase from Saccharomyces cerevisiae with protein phosphatase activity.

In this paper, specific PHO13 alkaline phosphatase from Saccharomyces cerevisiae was demonstrated to possess phosphoprotein phosphatase activity on the phosphoseryl proteins histone II-A and casein. The enzyme is a monomeric protein with molecular mass of 60 kDa and hydrolyzes p-nitrophenyl phosphate with maximal activity at pH 8.2 with strong dependence on Mg2+ ions and an apparent Km of 3.6 x 10(-5) M. No other substrates tested except phosphorylated histone II-A and casein were hydrolyzed at any significant rate. These data suggest that the physiological role of the p-nitrophenyl phosphate-specific phosphatase may involve participation in reversible protein phosphorylation. 1988 Federation of European Microbiological Societies.

Alkaline Phosphatase↗
PubMed1974

An assessment of serum acid and alkaline phosphatase determinations in prostatic cancer with a clinical validation of an acid phosphatase assay utilizing adenosine 3'-monophosphate as substrate.

Serum acid phosphatase (AcPase) was measured by a colorimetric method utilizing adenosine 3' -monophosphate as substrate in 389 patients. In about half the cases blood was taken shortly after a rectal examination. The upper reference limit (mean + 2SD) for 116 cases with miscellaneous illness after eliminating outliers was 4.1 International Units per litre (U/I) at 37 degrees C, and no correlation existed between AcPase activity and age in these subjects (r = 0.040). Eight of 18 patients with untreated carcinoma confined within the prostate gland had AcPase activities below 4.1 U/l, and all of 27 cases with extension to pelvic soft tissues or to bone exceeded this value. AcPase activities above 4.1 U/l were found in 6% of cases with benign hypertrophy of the prostate, in 5% of cases with non-prostatic cancer, and in none of 22 cases with other urological illness. Raised serum alkaline phosphatase (APase) activity was found in 60% of patients with untreated prostatic cancer and in only 6% of patients free of prostatic cancer, in most of whom there was a clinical explanation for the elevation. The correlation between the two phosphatase activities was not significant (r = 0.294). While APase activity does not reflect the stage of the disease as closely as AcPase activity, and is not so frequently elevated, it provided useful confirmation of the diagnosis in five patients of the present series whose AcPase levels were normal or only minimally elevated.

Acid Phosphatase↗
PubMed1991

Deficiency in phosphorylase phosphatase activity despite elevated protein phosphatase type-1 catalytic subunit in skeletal muscle from insulin-resistant subjects.

Glycogen synthase is activated by protein phosphatase type-1 (PP-1). The spontaneous PP-1 activity accounts for only a small fraction of total PP-1 activity, which can be exposed by trypsin digestion of inhibitor proteins in the presence of Mn2+. We determined total PP-1 activity in muscle biopsies from insulin-sensitive and -resistant nondiabetic Pima Indians. Inhibitor-2 sensitive PP-1 represented 90% of total phosphatase activity. Spontaneous and total PP-1 activities were reduced in insulin resistant subjects (P less than 0.05-0.01), suggesting that the reduced PP-1 activity is not the result of inhibition by trypsin-labile phosphatase regulatory subunits. This difference was further investigated by Western blots using two different antibodies. An antibody raised against the rabbit muscle PP-1 catalytic subunit was used to analyze muscle extracts concentrated by DEAE-Sepharose adsorption. An antibody raised against a peptide derived from the COOH-terminal end of the PP-1 catalytic subunit was used to analyze crude muscle extracts. Both antibodies recognized a PP-1 catalytic subunit of approximately 33 kD, which unexpectedly was more abundant in insulin-resistant subjects (P less than 0.05-0.01). The increase in the tissue PP-1 protein content may be a response to compensate for the impairment in the enzyme activity.

Adult↗
PubMed1998

Isolation of the human genes encoding the pyst1 and Pyst2 phosphatases: characterisation of Pyst2 as a cytosolic dual-specificity MAP kinase phosphatase and its catalytic activation by both MAP and SAP kinases.

We have isolated the human genes encoding the Pyst1 (MKP-3) and Pyst2 (MKP-X) MAP kinase phosphatases. Both genes consist of three exons interrupted by two introns and lack an intron which is conserved in all the other members of this gene family characterised to date. This reinforces the conclusion that Pyst1 and Pyst2 are members of a distinct and structurally homologous subfamily of dual-specificity (Thr/Tyr) MAP kinase phosphatases. We find that Pyst2 mRNA is constitutively expressed in a wide variety of human cell lines including those derived from ovarian, bladder and breast cancers. While there is no evidence for inducible expression of Pyst2 mRNA in human skin fibroblasts in response to cellular stress, Pyst2 mRNA levels are moderately increased in response to serum stimulation. Pyst2 protein is predominantly cytosolic when expressed in COS-1 cells. In common with Pyst1, Pyst2 shows substrate selectivity for the classical p42 (ERK2) isoform of MAP kinase both in vitro and in vivo, displaying much reduced activity towards stress activated MAP kinase isoforms such as JNK-1 and p38/RK. Pyst2 binds p42 MAP kinase in vivo and both MAP kinase binding and substrate selectivity correlate with the ability of different recombinant MAP and SAP kinases to cause catalytic activation of the Pyst2 phosphatase in vitro.

Animals↗