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)

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.
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PMID:Purification and characterization of a higher-molecular-mass form of protein phosphotyrosine phosphatase (PTP 1B) from placental membranes. 164 96

A full-length cDNA for a novel isoform of the human receptor tyrosine phosphatase gamma gene (PTPRG) was overexpressed in Sf9 insect cells, and the gene product, PTP gamma, was purified and characterized. The protein was expressed as a M(r) approximately 185,000 protein accompanied by a M(r) approximately 120,000 putative cleavage product on SDS-PAGE analysis. The protein undergoes N-linked glycosylation and constitutive phosphorylation of serine residues. When assayed for tyrosine-specific phosphatase activity, PTP gamma dephosphorylated myelin basic protein at a pH optimum of 7.5 and a Km of 12.6 microM; reduced carboxyamidomethylated and maleylated lysozyme (RCM-lysozyme) at a pH optimum of 6.0 and a Km of 12 microM; and p-nitrophenylphosphate with a pH optimum of 5.5 and a Km of 3.5 mM. Phosphatase activity was inhibited by ZnCl2 and sodium orthovanadate; Mg2+, Mn2+, and Ca2+ ions were ineffective. The partially purified form of the enzyme was allosterically activated by triphosphorylated nucleosides, with a preference for purines. This activation was prevented by Mg2+ addition and did not occur when a purified form of the enzyme was utilized, suggesting that its activation depends on specific activating factors or conformational constraints. Interestingly, PTP gamma protein was specifically bound by an ATP-agarose matrix through its intracellular domain, suggesting a link between binding of nucleotides and activation of the phosphatase.
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PMID:Characterization of the receptor protein tyrosine phosphatase gene product PTP gamma: binding and activation by triphosphorylated nucleosides. 758 20

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

The mechanisms for substrate recognition by two cytoplasmic protein tyrosine phosphatases, PTP-5 and rrbPTP-1, were investigated. Phosphorylation sites on tyrosine-phosphorylated casein, a model PTP substrate, were characterized. Two peptides based on casein phosphorylation sites and one peptide based on the tyrosine phosphorylation site of reduced, carboxamidomethylated and maleylated (RCM) lysozyme were tested as PTP substrates. The three peptides were dephosphorylated by PTP-5 and rrbPTP-1 at rates comparable to those of the corresponding sites on the intact proteins. This indicates that peptides based on the two model PTP substrates, casein and RCM-lysozyme, contained all or most of the structural information necessary for PTP-5 and rrbPTP-1 substrate recognition. Structural elements required for substrate recognition by PTP-5 and rrbPTP-1 were also investigated. Km values for dephosphorylation of three simple aromatic phosphate esters (phosphotyrosine, p-nitrophenyl phosphate, and phenyl phosphate) by rrbPTP-1 were about 5000-fold higher than those obtained for the peptide and protein substrates. This indicates that recognition of protein and peptide substrates involves structural elements in addition to the phosphate group and the aromatic tyrosine ring of phosphotyrosine. Analysis of the effects of truncations and Ala for polar substitutions on the reactivity with PTP-5 and rrbPTP-1 of peptides based on casein, RCM-lysozyme, and angiotensin II indicated that Asp or Glu within the first five residues on the N-terminal side of phosphotyrosine increased peptide reactivity with both PTP's. Asn residues were unable or only weakly able to substitute for Asp residues.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Acidic residues are involved in substrate recognition by two soluble protein tyrosine phosphatases, PTP-5 and rrbPTP-1. 824 Nov 30

The first example of a chicken cDNA sequence encoding a phosphotyrosyl phosphatase (PTPase) has been identified and found to contain coding sequences for the entire cytoplasmic and membrane spanning domains as well as a portion of the extracellular region of a transmembrane PTPase resembling human PTP zeta. Like HPTP zeta, chicken PTP zeta contained two phosphatase domains (D1 and D2), and D2 lacked a critical cysteine residue required for catalytic activity. The entire intracellular portion of CPTP zeta was expressed in bacteria and shown to be capable of dephosphorylating both p-nitrophenylphosphate and reduced carboxyamidomethylated and maleyated lysozyme but not phosphoseryl casein. Genetic analysis indicated that the presence of D2 was required for full activity. CPTP zeta mRNA was identified as a single large transcript expressed exclusively in the brain of chick embryos at both early and late stages of embryogenesis. These results suggested that CPTP zeta may perform a brain-specific function and have a role in development.
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PMID:Isolation of chicken phosphotyrosyl phosphatase cDNA sequences and identification of a brain-specific species related to human PTP zeta. 829 38