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H Metzger

Publications and source records attributed to H Metzger.

At least 145 records · Page 8Linked to original sources
PubMed1982

Proteolysis of soluble IgE-receptor complexes: localization of sites on IgE which interact with the Fc receptor.

Mouse and rat IgE and the respective soluble IgE-receptor complexes purified from rat basophilic leukemia cells were digested with trypsin. The end product in each case was F(ab')2-like. It contained the Ce2 regions, had intact antigen combining sites but had lost all ability to bind to the cell receptor for IgE. With mouse IgE the two principal sites of cleavage are likely to be the interdomain regions between Ce4:Ce3 and Ce3:C32 respectively. Cleavage at these sites occurs sequentially with the rate constant for the cleavage at the second site being approximately four-fold greater than that for the initial cleavage. When IgE is bound to the receptor the rates of cleavage are inhibited approximately three-fold. With rat IgE, the principal initial cleavage occurs within the intrachain disulfide loop in the Ce3 domain. Even when this disulfide bond in the digested protein is reduced, the product retains a substantial binding activity. A second cleavage occurs at a similar rate as the first and at a site analogous to that seen with mouse IgE, i.e. between the Ce3 and Ce2 domains. Notably, when bound to the receptor, the rate of cleavage at the first site is inhibited approximately three-fold but at the second site more than or equal to 40-fold. These results strongly implicate thd Ce3 domain as the principal site of interaction between rodent IgE and its receptor.

Amino Acid Sequence↗
PubMed1982

Further characterization of the beta-component of the receptor for immunoglobulin E.

A 30,000 mol. wt component (beta) is associated in a 1:1 ratio with the 50,000 mol. wt glycoprotein (alpha) which binds immunoglobulin E (IgE) on mast cells and related tumor cells. We show that alpha and beta are associated in membrane preparations. This is consistent with previous results which showed labeling of beta with the hydrophobic probe 5-iodonaphthyl-1-azide (INA). The beta-polypeptide is susceptible to proteolytic cleavage during preparation of the membranes and when this occurs a 20,000 fragment can be labeled with INA and remains associated with alpha. No incorporation of carbohydrate precursors into beta was observed. Since beta is also not modified when cells are surface-labeled, it may not be exposed on the cell surface. Rigorous washing of IgE-receptor complexes with non-ionic detergent results in dissociation of beta from the alpha-IgE complex. The latter will then not reassociate with beta when exposed to crude detergent extracts of the tumor cells.

Animals↗
PubMed1982

Binding of immunoglobulin E to the receptor on rat peritoneal macrophages.

The binding of radiolabeled monomers and chemically cross-linked dimers of rat immunoglobulin E (IgE) to peritoneal macrophages of rats was characterized. With either form, 40,000 to 50,000 molecules of IgE were specifically bound per cell under conditions where no endocytosis occurred. Monomeric IgE dissociated from macrophages within minutes, whereas dimers of IgE had a much slower rate of dissociation. Denatured rat IgE or native human IgE failed to inhibit the binding, but mouse IgE and, to a limited extent, rat IgG did. Oligomers of IgE by virtue of their tighter association with the receptor should prove useful in isolation of the receptor.

Animals↗
PubMed1982

Structure of the high-affinity mast cell receptor for IgE.

Mast cells and related rat tumor basophils have a surface receptor that binds monomeric IgE with high avidity. The receptor in situ is unclustered, mobile, and univalent, and its aggregation into dimers and higher oligomers triggers degranulation. It has two subunits, alpha and beta. The alpha chain has a molecular weight of about 50,000, of which 30% is carbohydrate. Heterogeneity in the latter accounts at least in part and perhaps fully for the heterogeneity of the alpha chain. Studies with proteases have delineated two domains: alpha 1 appears slightly larger on sizing gels, and incorporation studies suggest it has more carbohydrate than alpha 2. The alpha 2 domain and a 24,000-dalton subfragment of it contain the principal site whose surface labeling is blocked by the presence of IgE. The alpha subunit is firmly but noncovalently bound to beta in a 1:1 complex in situ and in detergent extracts. Nevertheless, during thorough washing of IgE-receptor complexes with detergent, beta dissociates. A portion of beta, beta 1, is integrated in the membrane; it is this domain that is labeled when the receptor is isolated from cells reacted with the intramembranous probe iodonapthylnitrene and that interacts with the alpha chain. These results and others have been used to draw a provisional model of the receptor.

Animals↗
PubMed1982

Calcium antagonists affect calmodulin-dependent contractility of a skinned smooth muscle.

The calcium antagonist prenylamine which had previously been found to inhibit fully the calmodulin myosin light chain kinase systems in concentrations of 200 mumol/l has now been found to inhibit the calmodulin-dependent contraction of skinned smooth muscle (guinea pig taenia coli). The inhibition by prenylamine is itself calcium-dependent. At maximum activation with Ca2+ and calmodulin, little inhibition is observed. Verapamil as well as prenylamine in small concentrations (less than 10 mumol/l) have been found to increase the rate of calcium-induced isometric tension development.

Animals↗
PubMed1981

Unexpected findings from target analysis of immunoglobulin E and its receptor.

The membrane receptor for immunoglobulin E (IgE) and its ligand, IgE, were irradiated with high-energy electrons. Loss of binding activity was measured for each, and the size of the functional targets was assessed. In both cases, the target size was substantially smaller than the covalent structure of the molecule. The direction of this discrepancy is unprecedented on the basis of experience with loss of enzymatic activity by irradiation; indeed, two enzymes which were present in the receptor preparations gave expected values when measured simultaneously. We suggest that in instances where a function such as ligand binding resides in a conformationally stable domain, radiation inactivation may be capable of revealing this.

Acetylglucosaminidase↗
PubMed1981

Enzymatic cleavage products of the alpha subunit of the receptor for immunoglobulin E.

The high-affinity membrane receptor for immunoglobulin E on mast cells and on a tumor analogue, rat basophilic leukemia cells, consists of two polypeptide chains: an alpha chain of Mr congruent to 50,000 and a beta chain of Mr congruent to 30,000. In this study we reacted alpha chains purified from tumor cells with proteolytic and glycolytic enzymes and compared the products by using differential labeling procedures. A variety of proteolytic enzymes cleave the chain into two similar-sized fragments, alpha 1 and alpha 2. The alpha 1 fragment behaves as if it were slightly larger on electrophoresis through polyacrylamide gels and is rich in carbohydrate as determined by incorporation of [14C]glucosamine. Less incorporation is observed into alpha 2 but it, like alpha 1, binds to concanavalin A. Labeling of the surface proteins on intact cells by lactoperoxidase-catalyzed iodination leads to preferential, perhaps exclusive, labeling of the alpha 2 fragment. The relative proportion of incorporated 3H-labeled amino acids and radioactive Bolton--Hunter reagent suggests that the polypeptide portions of alpha 1 and alpha 2 are similar in size. From these and other data we propose that the alpha chain may be U-shaped. Results from endoglycosidase digestions show that the receptor as isolated is heterogeneous because of variable glycosylation.

Animals↗
PubMed1981

Secretion from rat basophilic leukaemia cells induced by calcium ionophores. Effect of pH and metabolic inhibition.

Previous experiments on the functional properties of rat basophilic leukaemia cells showed a major anomaly when compared to normal mast cells: though IgE-mediated secretion was dependent on external Ca2+ with both types of cells, substantial non-cytotoxic release with ionophore A23187 could be demonstrated with the normal cells but not with the tumour cells. We now show that when the pH of the incubation medium is increased to 8 it is possible to obtain excellent Ca-dependent, non-cytotoxic secretion from tumour basophils with the ionophores A23187 and ionomycin. These results provide further evidence that secretion from the tumour cells occurs via a mechanism similar to that used by normal mast cells and basophils. Experiments with metabolically inhibited tumour cells suggest that their unusual sensitivity to the cytotoxic effects of Ca2+ ionophores may be related to their ability to sequester intracellular calcium. Changes in the conditions of cell culture appeared to produce substantial and at least partially reversible changes in responsiveness to IgE-mediated triggering and ionophores.

Animals↗
PubMed1981

Reaction of 5-iodonaphthyl-1-nitrene with the IgE receptor on normal and tumour mast cells.

Mast cells, basophils and a tumour analogue--rat basophilic leukaemia (RBL) cells--have a surface glycoprotein (R epsilon) which specifically binds monomeric immunoglobulin E (IgE), and aggregation of R epsilon causes secretion. When isolated from non-ionic detergent extracts of surface-labelled RBL cells by IgE-specific immunoprecipitation R epsilon appears as a 50,000 (50 K) to 60,000 (60 K) molecular weight (MW) band on electrophoresis in polyacrylamide gels in SDS (SDS-PAGE). Likewise, only a 50 component is observed when the polypeptide that binds IgE is isolated by affinity chromatography in conditions which prevent aggregation of the IgE, even when intrinsically labelled R epsilon is studied. To determine how R epsilon is inserted into the plasma membrane, we reacted RBL cells with the photolysable hydrophobic reagent 5-iodonaphthyl-1-azide (INA), which preferentially labels the intramembranous segments of several intrinsic membrane proteins. We report here that, surprisingly, the label was found, not on the 50 K glycopeptide, but only on a 30 K component which other studies suggest is a subunit of R epsilon (ref 9, 12).

Animals↗
PubMed1981

[Neuroradiology of the normal and pathological anatomy of the rat brain.--III Morphology and growth behaviour of experimental brain tumours following radiation therapy (author's transl)].

Radiation induced (30 Gy) morphological changes of experimental malignant brain tumors, which were produced by chemical carcinogenesis, were investigated by microangiography and correlated with the histological findings in 62 BD-IX-rats. In randomized groups the investigations were performed 2, 3, 6 and 8 weeks after the radiation was finished. Morphologically different reactions could be differentiated: remissions or partial recovery of the tumors, rest or recurrent tumor and uninfluenced tumor growth. The characteristic findings, the reasons for different courses and possible conclusions concerning the radiotherapeutical effect are discussed.

Animals↗
PubMed1981

[The value of radiometry in the treatment planning of inoperable carcinomas of the cervix (author's transl)].

A retrospective study of 731 patients with carcinoma of the cervix in various stages showed that recurrences were most common in patients treated with combined local radium application and irradiation of the parametrium. The basis for radiation treatment planning had been radiometry after the radium application. A comparison of the position of the uterus as shown by this method with computer tomography carried out in 40 patients in the position used for irradiation showed that in more than half these patients there was a significant difference in the results. It therefore appears that it is necessary to determine the position of the uterus by computer tomography in all patients if the applicator deviates from the median line by more than 10 degrees and if the parametrium is not fixed. Frequently it is possible, at an advanced stage, to use a rotational method instead of repeated radium applications.

Brachytherapy↗
PubMed1981

Qualitative characteristics of histamine release from human basophils by covalently cross-linked IgE.

We have studied the effects of permanent oligomers of human IgE produced using the cross-linking reagent, dimethyl suberimidate, on histamine release from human basophils. IgE dimers were found to be sufficient stimuli for both release and desensitization of these cells; monomeric IgE had no effect. Histamine release was augmented by deuterium oxide (D2O) in the medium, but D2O was not an absolute requirement to observe release. Desensitization by the dimeric IgE was specific in that the response to anti-IgE was not affected by preincubation of the leukocytes with the IgE dimer under suboptimal releasing conditions. IgE trimers and higher oligomers of IgE also caused both release and desensitization. IgE trimers were 3- to 4-fold more effective than IgE dimers with regard to the amount required for 50% histamine release. Dilution studies with monomeric IgE suggested that the difference was due to the presence of more "active" dimers in the trimeric IgE fractions. We conclude that dimeric IgE, by juxtaposing 2 receptors on the basophil membrane, is the "unit signal" for both release and desensitization of these cells.

Animals↗
PubMed1981

The positive inotropic-acting forskolin, a potent adenylate cyclase activator.

Forskolin is a positive inotropic-acting and blood pressure lowering agent which was isolated from the Indian plant Coleus forskohlii. In isolated heart tissue, forskolin activates a membrane bound adenylatecyclase and a cytoplasmic cAMP-dependent protein kinase to a much higher degree than does isoprenaline. This activation does not require the hormone receptor. In isolated and electrically stimulated left guinea pig atria, the adenylate-cyclase activation by forskolin is the prerequisite for the positive inotropic effect. We therefore postulate the adenylatecyclase activation to be correlated with the positive inotropic effect via an enhanced calcium uptake by the heart muscle cell.

Adenylyl Cyclases↗
PubMed1980

Composition and subunit structure of the cell receptor for immunoglobulin E.

The principal surface glycoprotein which specifically binds immunoglobulin E was isolated from rat basophilic leukemia cells in sufficient amounts for compositional and end group analyses. The protein has about 30% carbohydrate and a relatively low content of hydrophobic amino acid residues. No NH2-terminal residue was found by standard methods. The data suggest a Mr approximately equal to 50,000. The latter value is calculated on the basis of 1 molecule of receptor binding 1 molecule of immunoglobulin E. New data confirmed this valence. We propose a provisional model in which the principal component which binds immunoglobulin E is a monomer which, in cells and in nondenaturing solvents, is associated in a 1:1 ratio with the polypeptide of Mr approximately equal to 30,000 recently defined by studies employing cross-linking reagents.

Amino Acids↗