Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:3.2.1.17 (lysozyme)
21,489 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The involvement of tyrosine phosphorylation in insulin action led us to hypothesize that increased activity of protein tyrosine phosphatases (PTPases) might contribute to insulin resistance in alloxan diabetes in the rat. Hepatic PTPase activity was measured using two artificial substrates phosphorylated on tyrosine: reduced, carboxyamidomethylated, and maleylated lysozyme (P-Tyr-RCML) and myelin basic protein (P-Tyr-MBP), as well as an autophosphorylated 48-kD insulin receptor tyrosine kinase domain (P-Tyr-IRKD). Rats that were made alloxan diabetic exhibited a significant increase in hepatic membrane (detergent-soluble) PTPase activity measured with P-Tyr-MBP, without a change in activity measured with P-Tyr-RCML or the P-Tyr-IRKD. The PTPase active with P-Tyr-MBP behaved as a high molecular weight peak during gel filtration chromatography. Characterization of this enzyme indicated it shared properties with CD45, the prototype for a class of transmembrane, receptor-like PTPases. Our results indicate that alloxan diabetes in the rat is associated with an increase in the activity of a large, membrane-associated PTPase which accounts for only a small proportion of insulin receptor tyrosine dephosphorylation. Nonetheless, increased activity of this PTPase may oppose tyrosine kinase-mediated insulin signal transmission, thus contributing to insulin resistance.
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PMID:Differential regulation of multiple hepatic protein tyrosine phosphatases in alloxan diabetic rats. 132 40

A 48-kDa human T-cell protein-tyrosine-phosphatase (TC.PTPase) and a truncated form missing an 11-kDa C-terminal segment (TC delta C11.PTPase) were expressed by using the baculovirus system and characterized after extensive purification. The full-length PTPase was restricted to the particulate fraction of the cells from which it could be released by a combination of salt and detergent. The enzyme was entirely specific for phosphotyrosine residues. It displayed a low level of activity toward phosphorylated, reduced, carboxamidomethylated, and maleylated lysozyme (RCML), but was 12 times more active toward phosphorylated myelin basic protein (MBP). By contrast, the 37-kDa form localized in the soluble fraction, and its activity toward RCML was 5 times higher than that observed with MBP. The autophosphorylated cytoplasmic domain of the EGF receptor served as substrate for both enzymes. Limited proteolysis of either protein gave rise to a 33-kDa fragment displaying the substrate specificity of the truncated form. These data lend further support to the view that the C-terminal segment of the T-cell PTPase serves a regulatory function, playing an important role in the localization and substrate specificity of the enzyme.
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PMID:Purification and characterization of a human recombinant T-cell protein-tyrosine-phosphatase from a baculovirus expression system. 164 66

Regulation of cell growth and metabolism by protein tyrosine phosphorylation involves dephosphorylation via the action of protein tyrosine phosphatases (PTPases). We have characterized the membrane PTPases in rat liver, monitoring their activity by measuring the dephosphorylation of P-Tyr-reduced, carboxyamidomethylated and maleylated lysozyme (P-Tyr-RCML) and P-Tyr-myelin basic protein (P-Tyr-MBP). Separation of membrane PTPases by poly (L-lysine) chromatography yielded three peaks of PTPase, termed I, II and III. PTPases I and II were most active with P-Tyr-RCML, whereas PTPase III showed greater activity with P-Tyr-MBP than with P-Tyr-RCML (ratio of activities 4:1). Separation of membrane proteins by gel-filtration chromatography yielded two peaks of activity. Based on substrate specificity, sensitivity to inhibitors and requirement for thiol-containing compounds, the activity peak with an Mr of approximately 400,000 corresponded to PTPase III, whereas that with an Mr of approx. 40,000 contained PTPases I and II. All three PTPases dephosphorylated epidermal growth factor receptors and insulin receptors, but only PTPases I and II were active with P-Tyr-asialoglycoprotein receptors. Although none of the above characteristics distinguished between PTPases I and II, only PTPase I reacted in a Western immunoblotting procedure with anti-peptide antibodies directed towards human placental PTPase. We conclude that the membrane fraction from rat liver contains at least three distinct PTPases.
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PMID:Hepatic protein tyrosine phosphatases in the rat. 184 53

Homogeneous preparations of a protein phosphatase that is specific for phosphotyrosyl residues (protein tyrosine phosphatase [PTPase] 1B) were isolated from human placenta and microinjected into Xenopus oocytes. This resulted in an increase in activity of up to 10-fold over control levels, as measured in homogenates with use of an artificial substrate (reduced carboxamidomethylated and maleylated lysozyme). Microinjected PTPase was stable for at least 18 h. It is distributed within the oocyte in a manner similar to the endogenous activity and is suggestive of an interaction with cellular structures or molecules located predominantly in the animal hemisphere. The phosphatase markedly retarded (by up to 5 h) maturation induced by insulin. This, in conjunction with the demonstration that PTPase 1B abolished insulin stimulation of an S6 peptide (RRLSSLRA) kinase concomitant with a decrease in the phosphorylation of tyrosyl residues in a protein with the same apparent Mr as the beta subunit of the insulin and insulinlike growth factor 1 receptors (M. F. Cicirelli, N. K. Tonks, C. D. Diltz, E. H. Fischer, and E. G. Krebs, submitted for publication), provides further support for an essential role of protein tyrosine phosphorylation in insulin action. Furthermore, maturation was significantly retarded even when the PTPase was injected 2 to 4 h after exposure of the cells to insulin. PTPase 1B also retarded maturation induced by progesterone and maturation-promoting factor, which presumably do not act through the insulin receptor. These data point to a second site of action of the PTPase in the pathway of meiotic cell division, downstream of the insulin receptor and following the appearance of active maturation-promoting factor.
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PMID:Effect of microinjection of a low-Mr human placenta protein tyrosine phosphatase on induction of meiotic cell division in Xenopus oocytes. 215 16

PTPA, a specific phosphotyrosyl phosphatase activator of the PCSH2 and PCSL protein phosphatases, was purified up to apparent homogeneity from Xenopus laevis ovaries and rabbit skeletal muscle and highly purified from dog liver. PTPA appears as a 40-kDa protein in gel filtration, as well as in sucrose gradient centrifugation, and as a 37-39-kDa protein doublet in SDS-PAGE. Its estimated cellular concentration of 0.75 microM in oocytes or 0.25 microM in rabbit skeletal muscle is suggestive of an important role in the regulation of the cellular PTPase activity. The PTPase activation reaction of the PCSL phosphatase is time-dependent, ATP and Mg2+ being essential cofactors [A50(ATP) = 0.12 mM in the presence of 5 mM MgCl2]. With RCM lysozyme as substrate, the specific activity of the PTPA-activated PCSL phosphatase is 700 nmol of Pi/(min.mg). The pH optimum of the PTPase shifts from 8.5-9 in basal conditions to a neutral pH (7-7.5), and the A50 for the essential metal ion Mg2+ is decreased (3 mM). The activation is rapidly reversed in the presence of the substrate, and more slowly after removal of ATP.Mg. The PTPA-activated PCSL phosphatase represents a major PTPase activity in the cytosol of X. laevis oocytes (at least 50% of the measurable PTPase with RCM lysozyme phosphorylated on tyrosyl residues). The PTPA activation is specific for the PTPase activity of the PCSL and PCSH2 phosphatases, without affecting their phosphoseryl/threonyl phosphatase activity. However, effectors of the phosphorylase phosphatase activity, such as polycations and okadaic acid, also influence the PTPase activity. Phosphorylase alpha inhibits the activated PTPase activity (I50 = 5 microM). The PTPase activity of the other oligomeric PCS phosphatases (PCSH1 and PCSM) is not influenced, suggesting an inhibitory role for some of their subunits. This activation is compared with the recently described PTPase stimulation of the PCS phosphatases by ATP/PPi [Goris, J., Pallen, C. J., Parker, P. J., Hermann, J., Waterfield, M. D., & Merlevede, W. (1988) Biochem. J. 256, 1029-1034] and by tubulin [Jessus, C., Goris, J., Cayla, X., Hermann, J., Hendrix, P., Ozon, R., & Merlevede, W. (1989) Eur. J. Biochem. 180, 15-22].
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PMID:Isolation and characterization of a tyrosyl phosphatase activator from rabbit skeletal muscle and Xenopus laevis oocytes. 215 85

Although CD45 resembles the low Mr protein tyrosine phosphatases (PTPases) from human placenta in its specificity for phosphotyrosyl residues and absolute dependence on sulfhydryl compounds for activity, it also exhibits a number of distinguishing features. Most notably, it displayed substrate specificity in vitro, preferentially dephosphorylating myelin basic protein, over the other substrates tested, with high specific activity. Limited trypsinization of CD45 generated active fragments of approximately 65 kDa that were apparently derived exclusively from the intracellular segment of the molecule. These retained high activity against myelin basic protein, suggesting that this is an intrinsic feature of the PTPase domains and not the result of secondary interactions between the substrate and the putative ligand binding structure. With reduced carboxamidomethylated and maleylated lysozyme as substrate, CD45 was stimulated up to 12-fold by basic compounds such as spermine; divalent metal ions were also stimulatory, most notably Zn2+, which was previously identified as a potent inhibitor of the low Mr PTPases. CD45 was phosphorylated to high stoichiometry by casein kinase-2 (up to 1.5 mol/mol) and also by glycogen synthase kinase 3 (approximately 0.3 mol/mol) and protein kinase C (approximately 0.1 mol/mol); in all cases, no alteration in enzyme activity was detected following these modifications. Autophosphorylated preparations of epidermal growth factor receptor, insulin receptor, and p56lck protein tyrosine kinases were also substrates for CD45 in vitro.
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PMID:CD45, an integral membrane protein tyrosine phosphatase. Characterization of enzyme activity. 216 57

Protein-tyrosine phosphatases (PTPases) play a key role in the regulation of insulin action. In order to identify PTPases in skeletal muscle, the major site of insulin-mediated glucose disposal in vivo, we purified PTPases from rat muscle tissue fractions by a series of column chromatographic techniques. PTPase activities were assayed by measuring the dephosphorylation of a rat insulin receptor kinase domain, derivatized lysozyme and p-nitrophenylphosphate, and the enzymes were further characterized by immunoblotting. Of the total PTPase activity in muscle homogenates, 51-64% was localized to the solubilized particulate fraction, with the specific PTPase activity 3.3-fold and 5.6-fold higher in the particulate fraction towards RCM-lysozyme or the insulin receptor, respectively. The major peak (> 75%) of PTPase activity in the particulate fraction was purified further to 700-fold; 75% of this activity passed through a Blue-3GA column and revealed immunoreactivity for both LAR and SH-PTP2. PTPase activity retained on the Blue-3GA column contained PTPase1B. The major peak (> 70%) from muscle cytosol was further purified to 1500-fold. After the Blue-3GA step, immunoblotting revealed both SH-PTP2 and PTPase1B in the cytosol fraction, but LAR was absent from this fraction. LRP (RPTP-alpha) was not detected by blotting the PTPase activities from the purified particulate or cytosol fractions. Immunodepletion studies demonstrated that LAR, SH-PTP2 and PTPase1B were quantitatively major PTPase activities in the initial muscle homogenate, together accounting for over 70% of the total activity towards RCM-lysozyme. These studies provide insight into the relative abundance and subcellular distribution of specific PTPases in muscle tissue that are involved in the regulation of reversible tyrosine phosphorylation in this tissue.
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PMID:Purification, identification and subcellular distribution of three predominant protein-tyrosine phosphatase enzymes in skeletal muscle tissue. 771 Oct 57

The receptor like PTPase, PTP mu, displays structural similarity in its extracellular segment to members of the immunoglobulin superfamily of cell adhesion molecules. The full length form of PTP mu (200 kD) and a construct expressing only the intracellular PTPase domain-containing segment (80 kD) were expressed in the baculovirus/Sf9 cell system, purified and characterized. Full length PTP mu was membrane associated while the truncated form was recovered in the soluble fraction. PTP mu preferentially dephosphorylated a reduced carboxamidomethylated and maleylated derivative of lysozyme (RCML) over other tyrosine phosphorylated substrates such as myelin basic protein (MBP) or the synthetic peptide EDNDYINASL. The enzymatic properties of the soluble, truncated form of the enzyme were examined in detail. The pH optimum was 7.5. It dephosphorylated RCML with a Km of 400 nM and a Vmax of 725 nmol/min/mg. This form of the enzyme was 2 fold more active than full length PTP mu. Trypsinization of the full length form inhibited activity. Vanadate and molybdate, potent tyrosine phosphatase inhibitors, abolished activity of the enzyme. Zn++ and Mn++ ions, polylysine, poly-glu/tyr, and spermine were also inhibitory.
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PMID:Purification and characterization of the human protein tyrosine phosphatase, PTP mu, from a baculovirus expression system. 793 45

Protein-tyrosine-phosphatases (PTPases) have been implicated in the regulation of certain tyrosine kinase growth factor receptors in that they dephosphorylate the activated (autophosphorylated) form of the receptors. In order to identify PTPases that potentially act on receptor targets in liver, we used the human leucocyte common antigen-related PTPase (LAR) cDNA [Streuli, Krueger, Hall, Schlossman and Saito (1988) J. Exp. Med. 168, 1523-1530] and isolated two closely related transmembrane PTPase homologues from a rat hepatic cDNA library. Both PTPases had large extracellular domains that contained three immunoglobulin-like repeats and eight type-III fibronectin repeats. Both enzymes had tandem homologous PTPase domains following a single hydrophobic transmembrane domain. One sequence encoded the rat homologue of LAR. The second PTPase, designated LAR-PTP2, had 79 and 90% identity with rat LAR in the respective cytoplasmic PTPase domains, with only 57% sequence similarity in the extracellular domain. The catalytic domains of LAR and LAR-PTP2 prepared by bacterial expression were active in dephosphorylating a variety of phosphotyrosyl substrates but did not hydrolyse phosphoserine or phosphothreonine residues of labelled casein. Both enzymes exhibited rapid turnover numbers of 4-7 s-1 for myelin basic protein and 78-150 s-1 for derivatized lysozyme. LAR and LAR-PTP2 displayed similar PTPase activity towards the simultaneous dephosphorylation of receptors of intact insulin and epidermal growth factor from liver membranes. These data indicate that there is a family of LAR-related PTPases that may regulate the phosphorylation state of receptor tyrosine kinases in liver and other tissues.
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PMID:Molecular cloning and expression of a unique receptor-like protein-tyrosine-phosphatase in the leucocyte-common-antigen-related phosphate family. 806 21

Stimulation of fibroblasts with serum growth factors results in the rapid activation of a set of immediate-early genes, among them 3CH134. We have purified a bacterially expressed form of the 3CH134-encoded polypeptide and demonstrated that it has intrinsic protein-tyrosine-phosphatase (PTPase; protein-tyrosine-phosphate phosphohydrolase, EC 3.1.3.48) activity in vitro. This activity is optimal at pH 7.5, is sensitive to vanadate and cysteinyl modifying agents, and is insensitive to a panel of serine/threonine phosphatase inhibitors. Purified 3CH134 protein displays a high degree of selectivity among the tyrosine-phosphorylated polypeptide substrates tested. Under our assay conditions, the rates of dephosphorylation are in the order EDNDYINASL peptide < myelin basic protein < reduced, carboxyamidomethylated, and maleylated lysozyme (RCML) < p42mapk. There is a 200-fold range in rates for these substrates, with p42mapk dephosphorylated 15-fold more rapidly than RCML. Although 3CH134 is most closely related to the tyrosine/serine dual-specificity phosphatase VH1, we failed to detect any 3CH134-directed activity on casein or RCML phosphorylated on serine/threonine residues by cAMP-dependent protein kinase. Since 3CH134 expression is controlled transcriptionally and posttranscriptionally, it may represent a class of PTPases whose activity is regulated at the level of protein synthesis and degradation.
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PMID:The growth factor-inducible immediate-early gene 3CH134 encodes a protein-tyrosine-phosphatase. 838 79


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