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

---

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

Purification of a major placental membrane protein phosphotyrosine phosphatase (PTP-I) through the use of a nonhydrolysable phosphotyrosine analogue affinity ligand has enabled identification of the enzyme as a single polypeptide of at least 46 kDa. This phosphatase specifically dephosphorylates phosphotyrosine-containing substrates, including the src peptide, the epidermal-growth-factor receptor tyrosine kinase and the non-receptor tyrosine kinase p56lck. The p56lck can be dephosphorylated by PTP-I at two tyrosine residues (Tyr-394 and Tyr-505), which are differentially phosphorylated in vitro and in vivo and have been suggested to modulate kinase activity. The activity of PTP-I towards these substrates indicates a possible function of regulation of cellular tyrosine phosphorylation pathways at the level of growth-factor receptor and/or oncogene/proto-oncogene tyrosine kinases. Kinetic analyses show that PTP-I exhibits a Km value of about 2 microM with either src peptide or reduced, carboxyamidomethylated and maleylated (RCM)-lysozyme as substrate, and is inhibited in a mixed competitive manner by the polyanions heparin and poly(Glu4,Tyr1). Sequencing of PTP-I peptides reveals almost complete identity with sequences within the N-terminal half of the 37 kDa non-receptor tyrosine phosphatase 1B. However, the size and amino acid composition of PTP-I are similar to that of a higher-molecular-mass form of PTP 1B predicted from cDNA cloning. These results suggest that the 37 kDa PTP 1B is a proteolysed form of PTP-I, and provide evidence that a larger form of PTP 1B exists in vivo, at least in association with placental membranes.
...
PMID:Purification and characterization of a higher-molecular-mass form of protein phosphotyrosine phosphatase (PTP 1B) from placental membranes. 164 96

The receptor-linked tyrosine phosphatase RPTP alpha from human brain (Kaplan, R., Morse, B., Huebner, K., Croce, C., Howk, R., Ravera, M., Ricca, G., Jaye, M., and Schlessinger, J. (1990) Proc. Natl. Acad. Sci. U.S.A. 87, 7000-7004) was expressed in insect cells following infection with recombinant baculovirus. Two major forms of the enzyme, with molecular sizes of 98 kDa and 114 kDa, were detected by immunoblot analysis. This heterogeneity could be ascribed to N-linked glycosylation on the basis of two lines of evidence; namely, blockage of glycosylation with tunicamycin in vivo and removal of carbohydrates by endoglycosidase F in vitro. The 114-kDa form was purified to homogeneity by chromatography on Superose 12 and Mono Q. Compared to the low Mr placenta and T-cell tyrosine phosphatases, RPTP alpha displayed a low optimum pH of 6 and a high Km in the micromolar range toward two artificial substrates (tyrosyl-phosphorylated myelin basic protein and modified lysozyme, respectively). Most effectors had a different and often an opposite influence on phosphatase activity depending on the nature of the substrate and the pH at which the assays were performed. Determination of Km and Vmax values for RPTP alpha suggests that the enzyme could exist in low and high substrate affinity states.
...
PMID:Characterization of a human recombinant receptor-linked protein tyrosine phosphatase. 164 88

Thiophosphotyrosyl protein and peptide substrate analogs were found to be potent and specific protein-tyrosine phosphatase inhibitors with IC50s in the range of 0.2-30 microM. The analogs were based on highly reactive substrates and included thiophosphotyrosyl forms of reduced carboxamidomethylated and maleylated lysozyme and peptides based on tyrosine phosphorylation sites of lysozyme, alpha s2-casein, and platelet-derived growth factor receptor. These analogs inhibited protein-tyrosine phosphatases from both the intracellular and transmembrane classes and from a variety of species ranging from a prokaryote (Yersinia enterolitica) to man. The extent of inhibition of phosphatase activity by a given analog varied with the phosphatase species. In contrast, protein kinases and protein-serine/threonine phosphatases were not significantly affected by these analogs. The mechanism of inhibition was investigated using rat brain protein-tyrosine phosphatase-1 as a prototype. These studies indicated that the inhibition was rapid and reversible and was competitive in nature. The Ki for inhibition by various thiophosphotyrosyl analogs was generally proportional to the apparent Km for the corresponding phosphorylated substrates. Unphosphorylated substrate molecules were generally much weaker inhibitors than the corresponding thiophosphotyrosyl substrate analogs. Taken together these results point to an active site-directed mechanism for inhibition. These specific inhibitory probes could be used to study substrate binding mechanisms as well as physiological roles of various protein-tyrosine phosphatases.
...
PMID:Thiophosphorylated substrate analogs are potent active site-directed inhibitors of protein-tyrosine phosphatases. 771 49

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.
...
PMID:Purification and characterization of the human protein tyrosine phosphatase, PTP mu, from a baculovirus expression system. 793 45

A431 cells grown as three-dimensional spheroids show growth stimulation in response to nanomolar concentrations of EGF in contrast to monolayer cultures that show inhibition. In investigating the alterations in EGF signal transduction that underlie this modification of the proliferative response, we have compared the expression of EGF receptors on A431 cells under these conditions and related our findings to tyrosine phosphorylation and the growth response. EGF receptors were measured by 125I-EGF binding to trypsin-dispersed cells. Unexpectedly, dispersion of the monolayers caused an 80% decrease in surface EGF receptor, although, after dispersion, EGF receptor was digested by trypsin with a half-life of 69 +/- 32 min. No evidence for a comparable loss of cellular EGF receptor was seen on trypsin dispersion of spheroids. After allowing for this effect, we found that the receptor density on nondispersed monolayers (5 x 10(6) per cell) was twentyfold greater than that on spheroids (0.25 x 10(6) per cell). EGF-induced tyrosine phosphorylation was confined to the outermost cells of the spheroid, although the presence of surface-expressed EGF binding sites could be demonstrated throughout the structure and the number of EGF receptors/cell on dispersed spheroid cells showed a single distribution peak by flow cytometry, with no evidence for more than one population. Using RCM-lysozyme as a substrate, tyrosine phosphatase activity in spheroids lay within the range observed in monolayer cultures. Autophosphorylation of the EGF receptor following EGF stimulation in monolayer cultures of A431 cells rose rapidly in the first 10 seconds and then slowly increased for at least 3 h. In spheroids, it reached a maximum within 10 seconds and then declined over 3 h. Since the microenvironment within a tumor resembles that in a spheroid, a similar reduction in surface EGF receptor expression may be expected in tumors relative to monolayer cultures, together with corresponding growth stimulation in response to EGF.
...
PMID:Adaptation of EGF receptor signal transduction to three-dimensional culture conditions: changes in surface receptor expression and protein tyrosine phosphorylation. 796 22

Using polymerase chain reaction methods, we cloned a 1.7-kilobase cDNA, denoted DdPTPa, that has high homology with other known eukaryotic protein tyrosine phosphatases. DdPTPa possess a 241-amino acid protein tyrosine phosphatase domain located in the C terminus, which exhibits a 39-43% amino acid sequence identity with published protein tyrosine phosphatases. Absence of a characteristic signal sequence and transmembrane domain suggests that DdPTPa is a nonreceptor type cytoplasmic protein tyrosine phosphatase. Southern blot analysis of genomic DNA indicates the presence of a multigene protein tyrosine phosphatase family in Dictyostelium. Northern blot analysis reveals four species of mRNA that hybridize to the DdPTPa probe, at least three of which are developmentally regulated. The entire coding sequence of DdPTPa was subcloned into the pET15-b vector and expressed in Escherichia coli. Affinity-purified DdPTPa protein efficiently dephosphorylates both p-nitrophenyl phosphate and tyrosine-phosphorylated reduced, carboxyamidomethylated, and maleylated lysozyme. A Dictyostelium transformant overexpressing DdPTPa does not develop normally. The overexpresser fails to aggregate, in contrast to the control transformant containing vector alone, and after 24 h gives rise to only a few abnormal slugs and small fruiting bodies.
...
PMID:Cloning and functional expression of a Dictyostelium discoideum protein tyrosine phosphatase. 822 77

We report the first characterization of plasma-membrane-bound tyrosine phosphatase activity in the haemoprotozoan. Trypanosoma brucei. Several enzymic properties of the membrane fraction were identical to other protein tyrosine phosphatases (PTPases), such as (a) insensitivity to inhibitors of other protein phosphatases, including tetramisole, sodium tartrate and okadaic acid, (b) inhibition by sodium vanadate, and (c) activation by spermidine. Additionally, T. brucei PTPase activity presented two novel features, an acidic pH optimum at pH 4.0-5.0 and a very low Km value (2.5 nM) for the specific synthetic substrate, Tyr(P)Raytide. Higher Km values of 170 nM for Tyr(P)-RCML (RCML, reduced, carboxamidomethylated and maleylated lysozyme) and of 3 mM for the non-specific inorganic substrate p-nitrophenyl phosphate, suggested that the PTPase activity of T. brucei was substrate specific. Reconstitution experiments on bloodstream-stage membrane proteins revealed that three polypeptides of 148, 115 and 72 kDa contained vanadate-inhibitable PTPase activity. Modulator assays revealed that the 72-kDa protein was responsible for the observed spermidine stimulation, but indicated that the modulator profile of the 148-kDa protein was most similar to the whole membrane fraction. Furthermore, the PTPase activity of T. brucei was life-cycle-stage regulated. Neither the whole membrane fraction nor the reconstituted proteins of the procyclic insect stage dephosphorylated tyrosine residues.
...
PMID:Characterization of a life-cycle-stage-regulated membrane protein tyrosine phosphatase in Trypanosoma brucei. 857 47

Two forms of protein tyrosine phosphatases were partially purified from the musculo-cutaneous layer of Ascaris suum. A 50-55-kDa soluble form of the phosphatase cross-reacted with antisera raised against human PTP-1B and TC-PTP. Like the enzyme of human origin the phosphatase from Ascaris exhibited a preference for anionic substrates (tyrosine-phosphorylated carboxymethylated and maleylated lysozyme) and was inhibited by micromolar concentrations of vanadate, molybdate, Zn2+, heparin, and poly(Glu4Tyr). As revealed by immuno-cytochemistry, the phosphatase was mainly localized and appeared equally distributed in the cytoplasm, apart from the myofibrils, possibly in loose association with cytoskeletal elements. A second tyrosine phosphatase of 180 kDa molecular mass was mainly found in detergent extracts from a microsomal fraction. It showed no cross-reactivity with antisera raised against soluble mammalian phosphatases and dephosphorylated a basic substrate (Tyr-phosphorylated myelin basic protein). It was resistant to common inhibitors of mammalian tyrosine phosphatases except Zn2+ and thiol reagents.
...
PMID:Protein phosphotyrosine phosphatases in Ascaris suum muscle. 881 64

Protein tyrosine phosphatases were analyzed in oocytes of Ascaris suum. Phosphatases dephosphorylating modified acidic lysozyme were present in high-molecular-weight form (M(r) > 600,000) and as a 50- to 55-kDa protein in the soluble fraction. The low-molecular-weight form of the phosphatase cross-reacted with an antiserum raised against human T-cell protein tyrosine phosphatase and was not distinguishable from the 50- to 55-kDa protein tyrosine phosphatase previously described in the muscular layer of the adult worms (B. Schmid et al. 1996, Molecular and Biochemical Parasitology 77, 183-192). The low-molecular-weight form was also present on immunoblots of high-molecular-weight protein tyrosine phosphatase preparations after denaturing electrophoresis. The same or a similar form of the tyrosine phosphatase was also found in detergent extracts from the pelletal fraction. In addition, another tyrosine phosphatase of 180 kDa molecular mass that dephosphorylated myelin basic protein was also found in extracts from the soluble compartment as well as in detergent extracts from the pelletal fraction. It showed no cross-reactivity with antisera raised against soluble mammalian phosphatases and was resistant to inhibition by vanadate. While the activities of the myelin basic protein-dephosphorylating protein phosphatase remained fairly constant during early development of the oocytes, the activity of the enzyme dephosphorylating modified lysozyme in the pelletal fraction decreased to less than 10% of the initial activity between days 3 and 28 of incubation. Immunocytochemical studies of unfertilized and developing Ascaris eggs revealed association of protein tyrosine kinase and protein tyrosine phosphatase with the egg shell, in addition to their presence in the neighborhood of mitochondria. The amount of enzyme changed with the stage of development. In the larval stage (21 days) protein tyrosine kinase had increased in the chitin layer of the shell and in the nuclei while the relative amount of tyrosine phosphatase decreased in accordance with the biochemical data.
...
PMID:Ascaris suum: protein phosphotyrosine phosphatases in oocytes and developing stages. 953 68

Human and animal exposure to particulate air pollution is correlated with airway mucus hypersecretion and increased susceptibility to infection. Seeking clues to the mechanisms underlying this pathology, we examined the effect of the particulate air pollutant residual oil fly ash (ROFA) on production of the major component of mucus, mucin, and the major antibacterial protein of the respiratory tract, lysozyme. We found that following in vitro exposure to ROFA, epithelial cells showed an increase in mucin (MUC5AC) and lysozyme (LYS) steady state mRNA. This upregulation was controlled at least partly at the level of transcription as shown by reporter assays. Experiments testing the ability of the major components of ROFA to mimic these effects showed that vanadium, a metal making up 18.8% by weight, accounted for the bulk of the response. A screen of signaling inhibitors showed that MUC5AC and LYS induction by ROFA are mediated by dissimilar signaling pathways, both of which are, however, phosphotyrosine dependent. Recognizing that the ROFA constituent vanadium is a potent tyrosine phosphatase inhibitor and that mucin induction by pathogens is phophotyrosine dependent, we suggest that vanadium-containing air pollutants trigger disease-like conditions by unmasking phosphorylation-dependent pathogen resistance pathways.
...
PMID:Lung mucin production is stimulated by the air pollutant residual oil fly ash. 1063 31


1 2 Next >>

---