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At least 19 recordsLinked to original sources
PubMed1976

Modified 5'-nucleotides resistant to 5'-nucleotidase: isolation of 3-(3-amino-3-carboxypropyl) uridine 5'-phosphate and N2, N2-dimethylguanosine 5'-phosphate from snake venom hydrolysates of transfer RNA.

A procedure for the quantitative measurement of the O2'-methylnucleoside constitutents of RNA has recently been developed in this laboratory (Gray, M.W. Can. J. Biochem. 53, 735-746 (1975)). This assay method is based on the resistance of O2'-methylnucleoside 5'-phosphates (pNm) (generated by phosphodiesterase hydrolysis of RNA) to subsequent dephosphorylation by venom 5'-nucleotidase (EC 3.1.3.5). In the present investigation, two base-modified 5'-nucleotides, each displaying an unusual resistance to 5'-nucleotidase, have been identified. These compounds have been characterized by a variety of techniques as N2, N2-dimethylguanosine 5'-phosphate (pm2/2G) and 3-(3-amino-3-carboxypropyl)uridine 5'-phosphate (p4abu3U). Because of their resistance to 5'-nucleotidase, pm2/2G and p4abu3U are isolated along with the pNm in the mononucleotide fraction of venom hydrolysates of transfer RNA. Under hydrolysis conditions, the stability of p4abu3U is comparable to that of a pNm, allowing quantitative assay of the nucleotide. The proportion (mean +/- SD) of p4abu3U in venom hydrolysates of wheat embryo and Escherichia coli tRNA has been determined to be 0.35 +/- 0.03 (n=5) and 0.14 +/- 0.02 (n=4) mol%, respectively. The absence of p4abu3U in venom hydrolysates of yeast tRNA implies the absence of the corresponding nucleoside in yeast tRNA, in agreement with existing data. The variable recovery of pm2/2G from venom hydrolysates of wheat embryo and yeast tRNA indicates that under hydrolysis conditions, this base-modified nucleotide is only partially resistent to 5'-nucleotidase. The complete absence of pm2/2G in venom hydrolysates of E. coli tRNA is consistent with the known absence of N2, N2-dimethylguanosine in this RNA. These observations demonstrate that resistance to 5'-nucleotidase is a necessary but not sufficient criterion for concluding that a 5'-nucleotide is O2'-methylated. When applied to wheat embryo ribosomal RNA, the analytical methods described in this report failed to reveal any compound having the distinctive charge properties of p4abu3U. It therefore appears that 1-methyl-3-(3-amino-3-carboxypropyl)pseudouridine, recently characterized as a constituent of the 18 S rRNA of Chinese hamster cells (Saponara, A.G. & Enger, M.D. Biochim. Biophys. Acta 349, 61-77 (1974)), may not be present in wheat embryo ribosomal RNA.

Guanine Nucleotides↗
PubMed1975

Simultaneous determination of 5'-nucleotidase and alkaline phosphatase activities in serum.

A simple method is described for the simultaneous determination of alkaline phosphatase (EC 3.1.3.1) and 5'-nucleotidase (EC 3.1.3.5) in serum. The method is based on the determination of inorganic phosphorus released by the action of the two enzymes on adenosine-5'-monophosphate at pH 9.5 (200 mmol/l tris-buffer) in the presence and absence of L-cysteine. This amino acid at a concentration of 2--10 mmol/l was found to be a specific inhibitor for alkaline phosphatase but with no effect on 5'-nucleotidase activity.

Adenosine Monophosphate↗
PubMed1975

[Alkaline phosphatases in human feces, intestinal mucosa and bile, and the occurrence of 5'-nucleotidase in feces (author's transl)].

Alkaline phosphatase (EC 3.1.3.1) in extracts of human feces resembles alkaline phosphatase in extracts of duodenal mucosa, except for its electrophoretic mobility in starch gel. It is very probable that the normal feces alkaline phosphatase derives from intestinal mucosa. Gall bladder alkaline phosphatase, which is markedly different, has not been found in normal feces. Some patients with acute viral hepatitis or protozoasis excrete an alkaline phosphatase which resembles gall bladder alkaline phosphatase and has the characteristics of 5'-nucleotidase (EC 3.1.3.5). The appearance of this enzyme correlates with low total alkaline phosphatase activity of the excreta.

Adult↗
PubMed1976

Insulin receptors of skeletal muscle: specific insulin binding sites and demonstration of decreased numbers of sites in obese rats.

A membrane preparation was obtained from rat striated muscle. The preparation used has been shown to contain plasma membranes by electron microscopy as well as by enrichment in specific activity of both a plasma membrane enzyme "marker" (5'-nucleotidase) and cell surface 125I-incorporated radioactivity. The characteristics of 125I-insulin binding to this striated muscle preparation were studied, and it was found that 125I-insulin readily and specifically binds to this membrane preparation. The binding reaction was time, pH, and temperature dependent with optimal steady-state binding conditions occurring at 20 degrees C and at pH 7.6. Under these conditions (20 degrees C, pH 7.6) skeletal muscle plasma membranes displayed little ability to degrade insulin. Binding of 125I-insulin was readily inhibited at physiologic concentrations of unlabeled insulin and the specificity of this receptor for insulin was demonstrated by finding that high concentrations of glucagon, b-LH, b-FSH, p-PRL, hCG, TSH, and HGH were without effect on 125I-insulin binding and that insulin analogues inhibited binding in proportion to their biologic activity. When membranes from older, fatter rats were compared to membranes from younger, lean animals, 5'-nucleotidase specific activity and insulin degrading activity were found to be comparable. On the other hand, insulin binding to membrane receptors was decreased 30%-40% in the older, fatter animals. Thus, these studies indicate that (1) specific insulin receptors exist in skeletal muscle plasma membranes, and (2) membranes from older, fatter rats have fewer receptors than those from younger, lean animals.

Age Factors↗
PubMed1976

Acid, neutral, and alkaline hydrolases in arthritic synovium.

The levels of six lysosomal enzymes (acid phosphatase, beta-acetylglucosaminidase, cathepsin D, beta-galactosidase, arylsulfatase A, and beta-glucuronidase) and four neutral and alkaline hydrolases (esterase, inorganic phyrophosphatase, alkaline phosphatase, and 5'-nucleotidase) were measured in osteoarthritic, rheumatoid and control synovia. All enzyme levels in diseased synovium except esterase values in osteoarthritis were significantly elevated compared with controls. The mean values of the group of acid hydrolases and the group of neutral and alkaline hydrolases in osteoarthritic synovia were 1.9- and 2.0-fold greater than those of control specimens. In rheumatoid synovia, the values were 4.2- and 4.5 fold greater than control for the same enzymes. Levels in rheumatoid synovia were significantly higher than those in osteoarthritic synovia with the exception of 5'-nucleotidase. Only a limited correlation between the extents of inflammation present in the synovia and the levels of a lysosomal marker enzyme (cathepsin D) was observed. These results demonstrate that whatever the mechanism, increased levels of acid hydrolases as well as certain neutral and alkaline hydrolases are present in osteoarthritic and rheumatoid synovia, and these enzymes are probably contained in the synovial lining cells.

Acetylglucosaminidase↗
PubMed1976

Laboratory aids to diagnosis--enzymes.

A summary is presented of those organ specific enzyme assays traditionally used in evaluation of the patient with cancer. In addition, the use of certain serum enzymes such as gamma-glutamyl transpeptidase, phosphohexose isomerase or 5'-nucleotidase as aids in following the course of the disease, particularly in patients with metastatic spread to the liver is outlined. Also considered is the utility of enzyme analysis in biopsy tissue, biologic fluids, and washings of body cavities. Newer enzymes are considered which might, in the future, be developed as diagnostic tools or as probes for the understanding of the etiology of cancer.

Acid Phosphatase↗
PubMed1976

Proteins of the hepatoma tissue culture cell plasma membrane.

The specificity of lactoperoxidase-catalyzed iodination for the proteins of the hepatoma tissue culture cell plasma membrane was examined by histochemical, biochemical, and cell fractionation techniques. Light microscope autoradiography of sectioned cells shows the incorporated label to be localized primarily at the periphery of the cell. Most of this label can be released from the cell by trypsin but not by collagenase or hyaluronidase. The label is recovered from the cells as either monoiodotyrosine or diiodotyrosine after hydrolysis of cell extracts with a mixture of proteolytic enzymes. The label co-purifies during cell fractionation with an authentic liver cell plasma membrane marker enzyme, 5'-nucleotidase. Thus, the incorporated iodide is itself a valid marker for those membrane polypeptides having tyrosine residues accessible to the lactoperoxidase. The polypeptide complexity of the purified plasma membrane was examined by high resolution dodecyl sulfate-polyacrylamide gel electrophoresis. At least 50 polypeptides in the membrane are accessible to iodination. These polypeptides probably represent the bulk of the protein mass of the membrane and iodinating them does not affect cell viability, growth rate, or cell function. Labeling experiments with fucose and glucosamine show that at least nine of the iodinated peptides may be glycoproteins.

Carcinoma, Hepatocellular↗
PubMed1976

Isolation from bovine brain of a fraction containing capillaries and a fraction containing membrane fragments of the choroid plexus.

Combined differential and density gradient centrifugation was used for the isolation of a capillary-rich fraction from the cerebral cortex and a brush border containing fraction from the bovine choroid plexus. The activities of gamma-glutamyl transpeptidase and several other marker enzymes were monitored during the fractionation procedure. Electron microscopic examination showed a membrane-rich fraction in the choroid plexus high in the gamma-glutamyl transpeptidase and 5'-nucleotidase activities. From the brain cortex, a capillary-rich fraction was obtained which was high in gamma-glutamyl transpeptidase and alkaline phosphatase activities. A histochemical examination showed gamma-glutamyl transpeptidase activity localized in the capillary walls.

Acid Phosphatase↗
PubMed1975

H+ transport and membrane-bound HCO - 3 ATPase in salivary duct epithelium.

An ATPase stimulated by HCO - ions and other oxybases and inhibited by SCN- has been found in main excretory duct of rat submaxillary gland, a tissue, capable of actively secreting HCO - 3 ions. No such ATPase was found in the rabbit duct, which normally does not secrete HCO - 3. The HCO - 3 ATPase was localized in the plasma membrane fraction of the homogenate, as evidenced by the marker 5'-nucleotidase. The activities of the HCO - 3 ATPase increased in metabolic alkalosis and decreased in metabolic acidosis in parallel to secretion of HCO - 3 and K+ ions by the duct epithelium. These findings provide further evidence that the membrane-bound HCO - 3 ATPase is involved in active H+/HCO - 3 transport.

Adenosine Triphosphatases↗
PubMed2026

A novel peptide encoded by circTLL1 drives osimertinib resistance in lung cancer by modulating the NT5C2/Ras/PI3K axis.

BACKGROUND: Acquired resistance to osimertinib, a third-generation EGFR tyrosine kinase inhibitor, remains a major clinical challenge in the treatment of non-small cell lung cancer (NSCLC). Although circular RNAs (circRNAs) have been increasingly implicated in drug resistance, most studies have focused on their canonical role as microRNA sponges, while their capacity to encode functional micropeptides remains largely unexplored. This study aimed to identify novel circRNAs involved in osimertinib resistance and to characterize their regulatory functions at the protein level. METHODS: Osimertinib-resistant (OR) NSCLC cell lines were established and validated. High-throughput RNA sequencing was performed to compare the circRNA expression profiles between parental and OR cells. The function of the candidate circRNA was assessed through a series of in vitro and in vivo experiments, including cell viability assays, apoptosis analysis, and xenograft mouse models. Mechanistic investigations involved mass spectrometry, co-immunoprecipitation and western blotting to explore its protein-coding potential and downstream signaling pathways. RESULTS: We identified a novel circRNA, termed circTLL1, that was stably and significantly upregulated in OR-NSCLC cells. Functionally, overexpression of circTLL1 promoted osimertinib resistance, whereas its knockdown restored drug sensitivity both in vitro and in vivo. Mechanistically, we discovered that circTLL1 harbors an open reading frame (ORF) that is translated into a novel 90-amino-acid protein, which we designated circTLL1-90aa. Further investigation revealed that circTLL1-90aa directly interacts with and promotes the degradation of 5'-nucleotidase, cytosolic II (NT5C2), thereby uncoupling nucleotide metabolism from its normal regulatory constraints. The consequent downregulation of NT5C2 leads to elevated GTP levels and leading to the sustained activation of the downstream Ras/PI3K/AKT signaling pathway. CONCLUSION: Our findings unveil a previously unrecognized circRNA/micropeptide/metabolism cascade underlying osimertinib resistance. The identification of the circTLL1-90aa/NT5C2/Ras/PI3K axis not only expands the functional repertoire of the non-coding genome but also provides new insights into the complexity of drug resistance. Given its selective upregulation in resistant cells, circTLL1-90aa holds promise both as a predictive biomarker for treatment stratification and as an actionable therapeutic target, offering a novel strategy to overcome osimertinib resistance in NSCLC patients.

Pyrimidines↗
PubMed1976

The subcellular distribution of adenylate and guanylate cyclases in murine lymphoid cells.

Membrane vesicles can be prepared from murine lymphoid cells by nitrogen cavitation and fractionated by sedimentation through nonlinear sucrose density gradients. Two subpopulations of membrane vesicles, PMI and PMII, can be distinguished on the basis of sedimentation rate. The subcellular distribution of adenylate and guanylate cyclases in these membrane subpopulations have been compared with the distribution of a number of marker enzymes. Approximately 20-30% of the total adenylate and guanylate cyclase activity is located at the top of the sucrose gradient (soluble enzyme), the remainder of the activity being distributed in the PMI and PMII fractions (membrane-bound enzyme). More than 90% of the 5'-nucleotidase and NADH oxidase activities detected in lymphoid cell homogenates are located in PMI and PMII fractions, whereas succinate cytochrome c reductase activity is detected only in the PMII fractions. In addition, beta-galactosidase activity is distributed in the soluble and PMII fractions of the sucrose density gradients. On the basis of the fractionation patterns of these various enzyme activities, it appears that PMI fractions contain vesicles of plasma membrane and endoplasmic reticulum, whereas PMII fractions contain mitochondria, lysomes, and plasma membrane vesicles. Approximately 30-40% of the adenylate and guanylate cyclase activities in PMII can be converted to a PMI-like form following dialysis and resedimentation through a second nonlinear sucrose gradient. Adenylate and guanulate cyclases can be distinguished on the basis of sensitivity to nonionic detergents.

Adenylyl Cyclases↗
PubMed1975

Properties of plasma membranes from granulation tissue with reference to extracellular matrix.

Treatment with neuraminidase decreased the activity of Na+,K+-activated Mg2+-adenosine triphosphatase in plasma membranes isolated from experimental granulation tissue but not that of 5'-nucleotidase or leucine-beta-naphthylamidase. A temporary lowering of the pH of the plasma membrane suspension to 2-3 inactivated all three enzymes, which remained inactive after the pH had been readjusted to 7.4. Addition of dextran preparations to the membrane suspension decreased the activity of adenosine triphosphatase. Ethanol (0.4%) had a similar effect. These marker enzymes of plasma membranes were not affected by additions of hyaluronate, chondroitin sulfate, protein polysaccharide or soluble collagen. Serotonin stimulated the adenosine triphosphatase activity slightly. About 10-20% of the protein in the plasma membrane preparation was extracted with EDTA. This "fuzzy coat" fraction yielded a distinct gel-electrophoretic protein pattern. Hyaluronidase was not helpful in cleaving this surface layer from the plasma membranes.

Adenosine Triphosphatases↗
PubMedDate not supplied

[Study of inosine transformation into 5'-inosinic acid by the culture of Pseudomonas trifoli].

The transformation of inosine into 5'-inosine acid by Pseudomonas trifolii cells was studied. The synthesis of 5'-inosine acid can be performed by both live intact and dry cells. The effectiveness of inosine phosphorylation depends on the ratio of the inosine and phosphate donor concentrations and the amount of cells. The temperature and pH effect on activity of nucleoside phosphotransferase, phosphomonoesterase and 5'-nucleotidase has been studied. The influence of surface active substances and metal ions on the synthesis of 5'-inosine acid has been investigated. Optimal conditions for the inosine transformation by the above culture have been established.

Cations, Divalent↗
PubMed1976

Transport mechanisms in isolated plasma membranes. Nucleoside processing by membrane vesicles from mouse fibroblast cells grown in defined medium.

Plasma membrane vesicles were isolated from a subline of L929 mouse fibroblasts grown on defined medium in the absence of serum. These vesicles were not significantly contaminated by mitochondria or endoplasmic reticulum. The isolation procedure, a modification of that originally developed by McKeel and Jarett (McKeel, D.W., and Jarett, L. (1970) J. Cell Biol. 44, 417-432) employs mechanical homogenization in isotonic medium followed by differential centrifugation. The resultant plasma membrane vesicles take up radioactivity when exposed to uniformly labeled nucleosides. Two subfractions of the plasma membrane were isolated, distinguished by their differing activity of 5'-nucleotidase and (Na+,K+)-stimulated ATPase, two well known plasma membrane enzyme markers. Uptake of nucleoside radioactivity was extensively studied in one subfraction; it was linear with time and membrane concentration over ranges used for the studies. Apparent Km values for uptake of radioactivity from adenosine, inosine, and uridine were 7.1 +/- 26 muM, respectively. Uptake of radioactivity from all three nucleosides exhibits a broad pH optimum from pH 7 to pH 9, but falls off rapidly at lower pH. N-Ethylmaleimide was an effective inhibitor of uptake of radioactivity from all three nucleosides; uptake of radioactivity from uridine is more sensitive than uptake of radioactivity from the purine nucleosides. Adenosine inhibited uptake of radioactivity from inosine more than from uridine. Inosine inhibited the uptake of radioactivity from adenosine, but uridine did not. Caffeine and 6-methylaminopurine riboside (6-N-methyladenosine differentially inhibit uptake of radioactivity from adenosine and inosine, and thus the vesicles apparently possess seperate transport systems for uptake of radioactivity from purine nucleosides and from uridine.

Adenosine Triphosphatases↗
PubMed1976

Biochemical studies of tast sensation. Binding of L-[3H]alanine to a sedimentable fraction from catfish barbel epithelium.

Large numbers of taste buds are distributed over the body surface of the channel catfish ictalurus punctatus, with the barbels having an especially high density. L-Alanine, as well as certain other amino acids, are taste stimuli in this animal. Epithelial tissue obtained by gentle scraping of the barbel surface was fractionated by differential centrifugation. A sedimentable fraction (P2) was prepared that was enriched in L[OH]alanine binding activity, the plasma membrane marker enzyme 5'-nucleotidase, and the mitochondrial marker succinate cytochrome c reductase, but not the microsomal marker NADH cytochrome c redu.ctase. Binding of L-[OH]alanine was measured using a Millipore filter method in which correction for non-specific binding was also determined. Time, temperature, and pH for measuring binding activity were established. At the optimal pH of 7.8, the KD for L-alanine is 4.8 X 10(-6) M. The first order dissociation rate constant at 6 degrees is 3.8 X 10(-4) s-1 and at 24 degrees it is 12.1 X 10(-4) s-1. The second order rate constant for association is between 10(2) and 10(3) M-1 S-1. Reversibility of the binding interaction was also demonstrates by the rapid displacement of bound L-[3H]alanine by a large excess of unlabeled L-alanine. That the binding does not represent incorporation into protein was confirmed by the lack of effect of puromycin. The amounts bound of several other chemostimulatory amino acids werealso determined.

Alanine↗