Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.4.21.4 (trypsin)
 42,187 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Receptors for human, simian, ovine, bovine and murine prolactin, human growth hormone and human placental lactogen have been identified in plasma-membrane-containing subcellular particles isolated from rabbit mammary glands. The association and dissociation of (125)I-labelled prolactin are time- and temperature-dependent processes, both being maximal at 37 degrees C. (125)I-labelled prolactin prepared by the enzymic iodination procedure with lactoperoxidase binds better to receptors than does the preparation obtained by using chloramine-t as the oxidizing agent. The binding of (125)I-labelled prolactin to receptors is strongly influenced by pH and ionic composition but not by many low-molecular-weight compounds tested, e.g. steroids, nucleotides and several drugs. Receptor activity is sensitive to trypsin and phospholipase C digestion, suggesting that protein and phospholipid moieties are essential for the binding of (125)I-labelled prolactin. The binding of (125)I-labelled prolactin to receptors is a saturable and reversible process. Scatchard and Lineweaver-Burk analyses suggest that (125)I-labelled prolactin has a high affinity for its receptor. Binding of (125)I-labelled prolactin to receptors does not result in the destruction of the hormone. Considerable prolactin-binding activity is also observed in subcellular fractions isolated from the adrenal gland, liver, ovary and kidney of the pregnant rabbit, a finding that is consistent with other reported actions of prolactin in these organs.
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PMID:Properties of a prolactin receptor from the rabbit mammary gland. 437 64

Mammalian cells transformed in tissue culture by SV40 were shown to contain, in addition to the SV40-coded 94,000 d large T antigen and the 20,000 d small t antigen, a approximately 56,000 d cellular protein, which specifically precipitates with sera of animals bearing SV40-induced tumor(s) (tumor or T serum). We investigated the presence of these three proteins at the surface of logarithmically growing SV40-transformed cloned mouse cells, after metabolic labelling with [35S]-methionine for 3 h. The 56,000 d protein was found to be susceptible to digestion by trypsin under conditions which did not disrupt the cells, while no small t antigen was found to be digested. Both the 56,000 d cellular protein and the SV40 large T antigen were susceptible to lactoperoxidase-catalyzed iodination from the outside of intact cells. Trypsin treatment removed both the iodinated 56,000 d protein and the iodinated SV40 large T antigen. These experiments indicated that (a certain amount of) the 56,000 d protein and a relatively small amount of the large T antigen (which is present mainly in the nucleus) are present on the cell surface. The results confirm and extend independent experiments using subcellular fractionation techniques (Luborsky and Chandrasekaran, 1980; Soule and Butel, 1979). After heat treatment (at 50 degrees C for 30 min) of the whole-cell extract the 56,000 d cellular protein was precipitated by the tumor serum in the absence of precipitation of SV40 large T antigen. This result showed that the 56,000 d protein is more (thermo)stable (in the whole-cell extract) than the SV40 large T antigen, and also indicated that the tumor serum employed had antibodies against the 56,000 d cellular antigen. The heat-treated whole-cell extract of Sv40-transformed mouse cells was able to immunize and fully protect mice against a lethal tumorigenic dose of SV40-transformed cells. These results suggest the need for further experiments to characterize the chemical and immunologic properties of the 56,000 d protein.
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PMID:Surface proteins of simian-virus-40-transformed cells. 616 62

Addition of ATP to medium surrounding intact, transformed 3T3 cells causes the formation of aqueous channels in the plasma membrane. This effect of extracellular ATP is sharply dependent on the pH and temperature of the incubation medium, and is inhibited by low levels of La3+ or ruthenium red; inhibition is also obtained with concentrations of Mg2+ ions that exceed a ratio of Mg/ATP of one. The effect of ATP on membrane channel formation is unaffected by chelators of metal ions or by prior modification of the cell surface with various surface-active enzymes or sulfhydryl reagents. Under conditions which favor aqueous channel formation, incubation of intact 3T6 cells with ATP (gamma-32P) leads to phosphorylation of two membrane components with apparent molecular weight of 40,000 (40K) and 110,000 (110K) daltons; the 110K component which is unaffected by trypsin under normal conditions is rendered trypsin-sensitive by the phosphorylation reaction, probably as a result of a conformational change. Conditions which inhibit aqueous channel formation also inhibit phosphorylation of the 110K protein and decrease the labeling of the 40K component. These results indicate the probable role of cell surface phosphorylation, involving one or both of these components, in the formation of aqueous channels in transformed 3T3 cells. Aqueous channel formation by extracellular ATP is not associated with gross unfolding of the cell surface as revealed by lactoperoxidase-catalyzed iodination of the 3T6 cell surface.
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PMID:Passive membrane permeability to small molecules and ions in transformed mammalian cells: probable role of surface phosphorylation. 625 85

The membranes from epidermoid carcinoma cells (A-431) that were surface iodinated while intact using catalysis by lactoperoxidase and 125I as iodide contain one major labeled protein of Mr = 180,000. This protein is clearly iodinated on the outside of the intact cell because it is not the major protein labeled when isolated membranes are iodinated. This major surface-iodinated protein is almost certainly the epidermal growth factor (EGF) receptor, since both have the same Mr and have identical sensitivity to proteases. Both are nearly quantitatively converted from an Mr = 180,000 form to an Mr = 160,000 form by an endogenous calcium-activated neutral protease when cells are broken in the presence of calcium. Both are degraded by trypsin only if trypsin has access to the inside of the cell. This latter finding implies that the surface-iodinated EGF receptor spans the plasma membrane. Since the EGF receptor is an autophosphorylating kinase whose activity is enhanced in the presence of EGF, the receptor was labeled and identified using [gamma-32P] ATP. While both iodination and EGF-enhanced phosphorylation occur on tyrosine residues, peptide mapping of the iodinated or phosphorylated Mr = 180,000 band showed that different peptides were being labeled. Since the EGF receptor-kinase spans the plasma membrane, the peptide iodinated on the surface of the intact cell must be different from the peptides that are probably autophosphorylated on the cytoplasmic side of the membrane.
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PMID:Surface iodination of epidermal growth factor receptors in intact cells. 632 89

The transferrin receptor is a 180 000-dalton protein which can be dissociated to two 90 000-dalton polypeptides under reducing conditions. It can be labelled by lactoperoxidase-catalysed iodination on the cell surface at 0 degree C. Trypsin digestion of labelled cells at 0 degree C can be used to degrade those receptors on the cell surface; they release a 70 000-dalton soluble fragment which binds to transferrin. When cells are labelled at 0 degree C, then warmed to 37 degrees C, the labelled receptors enter the cells and become trypsin resistant. These receptors enter the cells, probably via coated pits, with a half-life of approximately 5 min. Since there is about three times as much receptor inside cells as on the surface, this means that transit through the cell to the cell surface takes approximately 21 min, if all receptors are on the same cycling pathway.
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PMID:Transferrin receptor and its recycling in HeLa cells. 632 61

A technique was developed for obtaining high yields of naturally released Plasmodium falciparum merozoites from synchronous cultures of parasitized erythrocytes. The cultured erythrocytes were treated with trypsin to prevent reinvasion (6), and the released merozoites that accumulated extracellularly were harvested by differential centrifugation. The total biosynthetically labeled proteins of schizonts and merozoites, and those immunoprecipitated by human immune serum were analyzed and compared. The surface antigens of free merozoites, labeled by lactoperoxidase-catalyzed iodination, were also described. A monoclonal antibody, specific for a 195,000 mol wt schizont protein, and processing fragments derived from it (3) were used in immunoprecipitation and Western transfer analyses to determine which of the processing fragments are associated with merozoites and which of them are located on the merozoite surface. It was found that processing of the 195,000 mol wt precursor down to an 83,000 mol wt fragment is complete in free merozoites, and that this fragment is expressed as one of the major surface antigens of P. falciparum merozoites.
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PMID:Surface antigens of malaria merozoites. A high molecular weight precursor is processed to an 83,000 mol wt form expressed on the surface of Plasmodium falciparum merozoites. 635 63

We have identified strain-specific antigens with Camp and St. Lucia strains of P. falciparum of Mr approximately 285,000 and approximately 260,000, respectively. These strain-specific antigens were metabolically labeled with radioactive amino acids, indicating that they were of parasite origin rather than altered host components. These proteins had the properties of a molecule exposed on the surface of infected erythrocytes (IE). First, the proteins are accessible to lactoperoxidase-catalyzed radioiodination of IE. Second, the radioiodinated proteins were cleaved by low concentrations of trypsin (0.1 microgram/ml). Third, these antigens were immunoprecipitated after addition of immune sera to intact IE. Fourth, the strain-specific immuno-precipitation of these proteins correlated with the capacity of immune sera to block cytoadherence of IE in a strain-specific fashion. Fifth, the strain-specific antigen had detergent solubility properties (i.e., insolubility in 1% Triton X-100, solubility in 5% sodium dodecyl sulfate) similar to the variant antigen of P. knowlesi, which has been proven to be a malarial protein exposed on the erythrocyte surface.
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PMID:Identification of a strain-specific malarial antigen exposed on the surface of Plasmodium falciparum-infected erythrocytes. 637 9

Insulin receptors of Fao hepatoma cells were labelled with a 125I-labelled photoreactive insulin analogue or by surface iodination catalysed by lactoperoxidase. Cells were then incubated at 37 degrees C, and the cellular localization of the labelled receptors was assessed by limited exposure of intact cells to trypsin. The results show that: (1) photolabelled insulin-receptor complexes are internalized and recycled in Fao hepatoma cells; (2) the dynamics of photolabelled insulin receptors (internalization and recycling) is similar before and after down-regulation; (3) the unoccupied receptors labelled by surface iodination are internalized and recycled similarly to covalent insulin-receptor complexes; (4) insulin does not induce internalization of surface-iodinated insulin receptors. We conclude that internalization and recycling of insulin receptors are independent of receptor occupancy by insulin in Fao hepatoma cells.
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PMID:Internalization and recycling of insulin receptors in hepatoma cells. Absence of regulation by receptor occupancy. 638 54

Two monoclonal antibodies that cause changes in the morphology of cultured chick myogenic cells have been described previously [8]. In this paper, these antibodies are shown to interact with the same 140Kd protein. The 140Kd protein has been further characterized as a cell-surface glycoprotein by lactoperoxidase-catalyzed iodinations and lectin affinity chromatography. The protein is resistant to digestion by trypsin and collagenase and has been shown to be unrelated to fibronectin by immunoprecipitation studies and by peptide mapping. A second protein, of approximately 170Kd MW, is also immunoprecipitated by the monoclonal antibodies. This protein is probably unrelated to the 140Kd protein since the peptide maps are quite distinct.
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PMID:Characterization of a 140Kd cell surface glycoprotein involved in myoblast adhesion. 638 44

A purification procedure for a protein related to lactoperoxidase devoid of the heme prosthetic group under conditions also yielding enzymatically active lactoperoxidase is described. These two forms were separated from bovine milk according to their respective behaviors on cation exchange. Lactoperoxidase and non-heme lactoperoxidase had the same apparent molecular weight in the denatured (sodium dodecyl sulfate-polyacrylamide gel electrophoresis) and native form (velocity sedimentation on sucrose gradient) about 85,000; but unlike lactoperoxidase, non-heme lactoperoxidase was devoid of light absorption properties in the Soret region and of enzyme activity. Lactoperoxidase and non-heme lactoperoxidase contained a similar amount of carbohydrate and gave very similar peptide maps after limited proteolysis by subtilisin or trypsin. The two forms appeared to be immunologically related since they gave a single line in immunodiffusion using anti-lactoperoxidase antibodies and since 125I-labeled non-heme lactoperoxidase and 125I-labeled lactoperoxidase reacted with anti-lactoperoxidase antibodies in radioimmunoassay. Lactoperoxidase and nonheme lactoperoxidase were compared in their ability to interact with diiodotyrosine and tubulin (Rousset, B., and Wolff, J. (1980) J. Biol. Chem. 255, 2514-2523). 125I-labeled diiodotyrosine bound specifically to lactoperoxidase. No detectable binding has been observed with nonheme lactoperoxidase. In contrast, lactoperoxidase and non-heme lactoperoxidase coupled to an insoluble matrix were able to bind rat brain tubulin, indicating that both forms of lactoperoxidase can be used for an affinity chromatography purification procedure of brain tubulin. Non-heme lactoperoxidase was found in milk from several origins, cow, goat, sheep, and human. In bovine milk, lactoperoxidase and non-heme lactoperoxidase were found in comparable amounts.
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PMID:Identification, purification, and characterization of a non-heme lactoperoxidase in bovine milk. 641 36


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