Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: HUMANGGP:036206 (endoplasmic reticulum)
 63,868 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The binding to isolated hepatocyte plasma membranes of radioactively labelled inhibitors of microfilamentous and microtubular protein function ([3H]cytochalasin B and [3H]colchicine, respectively) was studied as one means of assessing the degree of association of these proteins with cell surface membranes. [3H]Cytochalasin B which behaved identically to the unlabelled compound with respect to binding to these membranes was prepared by reduction of cytochalasin A with NaB3H4. The binding was rapid, readily reversible, proportional to the amount of membrane and relatively insensitive to changes of pH or ionic strength. At 10(-6) M [3H]cytochalasin B, glucose of p-chloromercuribenzoate, an inhibitor of glucose transport inhibited binding by about 20%; treatment of membranes with 0.6 M KI which depolymerizes F actin to G actin caused about 60% inhibition of binding. These two types of inhibition were additive indicating two separate classes of binding sites, one associated with sugar transport and one with microfilaments. Filamentous structures with the diameter of microfilaments (50 A) were seen in electron micrographs of thin sections of the membranes. At concentrations greater than 10(-5) M [3H]cytochalasin B, binding was proportional to drug concentration, characteristic of non-specific adsorption or partitioning. Intracellular membranes of the hepatocyte also bound [3H]cytochalasin B, those of the smooth endoplasmic reticulum to a greater extent than plasma membranes. [3H]Colchicine bound to plasma membranes in proportion to the amount of membrane and at a rate compatible with binding to tubulin. However, other properties of the binding including effects of temperature, drug concentration and antisera against tubulin were different from those of binding to tubulin. Hence, no evidence was obtained for association of microtubular elements with these membranes. Despite this there appeared to be an interdependence between microtubule and microfilament inhibitors: vinblastine sulfate stimulated [3H]cytochalasin B binding and cytochalasin B stimulated 3H colchicine binding. [3H]Colchicine also bound to intracellular membranes, especially smooth microsomes.
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PMID:Binding of [3H]ctyochalasin B and [3H]colchicine to isolated liver plasma membranes. 1 29

1. Three soluble polysaccharides and a soluble protein containing hydroxyproline were secreted by sycamore suspension cultures. l-[1-(3)H]Fucose was incorporated solely into the fucose of fucoxyloglucan and l-[1-(14)C]arabinose mainly into the arabinose of arabino-galactan. [U-(14)C]Glucose was a general precursor for soluble protein and polysaccharides. 2. The steady-state rate of secretion of all the polymers was increased within seconds of adding various electrolytes and polyelectrolytes to the growth medium. The increased secretion was induced by cations at the outer surface of the plasma membrane. It was brought about by a stimulation of the normal mechanisms of cell-wall polysaccharide secretion. It was partly inhibited by anaerobiosis or sodium arsenate and was unaffected by temperature changes in the range 0-35 degrees C. 3. The precursor pool from which secretion was induced contained completely synthesized polysaccharides and was probably located in the Golgi-derived vesicles. The results indicated that the endoplasmic reticulum did not secrete polysaccharide directly to the cell exterior. 4. The various cations probably induced secretion by causing a depolarization of the negative electric potential of the cell surface, and this resulted in the fusion of vesicles with the plasma membrane. 5. Analogy with exocytosis and pinocytosis in various animal tissues suggested that the decreased surface potential brought about membrane fusion by causing an increase in plasma-membrane permeability to Ca(2+). 6. The results showed that the fusion of vesicles with the plasma membrane was rate-limiting and a potential control point. Auxin-stimulated cell-wall deposition could be a result of a stimulated influx of Ca(2+) causing vesicle fusion with the plasma membrane.
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PMID:Influence of cations at the plasma membrane in controlling polysaccharide secretion from sycamore suspension cells. 2 5

alpha-glucosidases are cellular enzymes, able to split the polysaccharides into glucose. In subcellular fractions from rat and trout hepatocytes, the distribution patterns of neutral alpha-glucosidase and of glucose-6-phosphatase appear to be very similar, i.e., closely linked to the endoplasmic reticulum, and are somewhat related to the particular glycogen. The data suggest a probable role of neutral alpha-glucosidase in cell physiology and in carbohydrates metabolism.
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PMID:[Similar distribution of the activities of neutral alpha-glucosidase (gamma-amylase) and glucose-6-phosphatase in subcellular fractions from rat and trout livers]. 3 99

The reversibility of changes in ultrastructure, K+, and ATP content was studied in experimental injury of Ehrlich ascites tumor cells. Different grades of injury resulted from incubations in N2 atmosphere and omitting substrate after which air and glucose were reinstated. The changes observed in cells after 1 hour of anoxia such as dilations of endoplasmic reticulum, complex invaginations of plasma membrane, and slight condensation of mitochondria, as well as a drop of K+ and ATP content to a level approximating 40 per cent of the paired controls, were entirely reversible. After 2 hours of anoxia approximately 50 per cent of the cells recovered, but after 3 and 4 hour of anoxia most of the cells were irreversibly damaged showing markedly swollen mitochondria with flocculent densities.
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PMID:Studies of cellular recovery from injury. I. Recovery from anoxia in Ehrlich ascites tumor cells. 5 20

In order to obtain plasma membrane-rich fractions two methods were tried. Approach A was based on differential pelleting followed by discontinous gradient centrifugation in a B-XIV zonal rotor. In approach B homogeneization was performed in buffered water (NaHCO3, pH 7.4). The 73 300 X g pellet from this homogenate was subjected to buoyant density equilibrium in a HS zonal rotor (continuous sucrose gradient). Using approach A, the highest relative specific activity for plasma membrane markers was found at the 30-37% sucrose interphase. However, an increase for glucose 6-phosphatase (endoplasmic reticulum marker) was also found at that interphase. Using approach B marker profiles different from approach A were found. Approach B results in a subdivision of membrane material in four distinct regions. These regions do not contain completely pure membrane species, although region I seems to be essentially derived from plasma membranes. It is also concluded from approach A that plasma membranes from bovine thyroid tissue are heterogeneous.
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PMID:Subcellular structure of bovine thyroid gland. VII. A study on the distribution of bovine thyroid plasma membranes by density gradient centrifugation in zonal rotors. 8 Jan 97

In bovine thyroid tissue the glucose 6-phosphatase activity is not entirely due to the presence of an unspecific acid phenylphosphatase nor to beta-glycerophosphatase. This glucose 6-phosphatase is very probably localized within endoplasmic reticulum membranes. It is not a good marker for distribution patterns obtained after differential pelleting. However it can be used as a marker for endoplasmic reticulum membranes after centrifugation in a zonal rotor.
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PMID:Occurrence and subcellular localization of glucose 6-phosphatase in bovine thyroid. 9 89

In an attempt to elucidate the biochemical mechanism of acetaminophen-induced hepatic necrosis, the present study in hamsters was undertaken to evaluate the possible changes in lipid peroxidation and microsomal enzyme activities. The protective action of cysteamine was likewise assessed in the light of these biochemical variables and the fine structural features of the liver were seen by electron microscopy. One group of golden Syrian hamsters was administered a toxic dosage of acetaminophen (600 mg . per kg . intraperitoneally) while another group was treated with the same dosage of acetaminophen, followed 1 hour later by cysteamine (200 mg . per kg . intraperitoneally). The animals were sacrificed at 6, 12, 18, and 24 hours. Microsomal fractions were isolated for biochemical assays, and liver sections were prepared for electron microscopy. Results showed that significant enhancement of lipid peroxidation occurred in the untreated acetaminophen-poisoned group, as compared to the cysteamine-treated group. Glucose 6-phosphatase activity was markedly suppressed at 6, 12, and 18 hours after acetaminophen administration. Cysteamine treatment completely prevented the curtailment of NADPH-cytochrome c reductase and glucose 6-phosphatase activities in the protected group, and partially maintained aniline hydroxylase activity. Cytochrome P-450 level was unaffected in both the cysteamine-treated and the untreated groups at the respective time intervals. Electron microscopic examination showed progressive loss of the structural integrity of the endoplasmic reticulum, lipid infiltration, and vacuolation in the untreated acetaminophen-poisoned group. At 18 and 24 hours, sinusoidal congestion and myeloid figure formation were prominent. In the cysteamine-protected group, polysomes reassembled around the granular endoplasmic reticulum at 18 hours. It is postulated that lipid peroxide formed in vivo may facilitate the microsomal oxidation of acetaminophen to the toxic metabolite. NADPH-cytochrome c reductase is likely to be the locus within the NADPH-cytochrome P-450 electron transport chain susceptible to lipoperoxidation. The free radical-related lipoperoxidation may mediate the impairment of in vitro drug metabolism, as reflected by the depressed aniline hydroxylase activity. The abnormal phospholipid metabolism is manifested at the fine structural level by the myeloid body formation. The protective effects of cysteamine as seen in the attenuated lipid peroxidation and the consequent derangement of microsomal enzymes correlate well with the morphologic observations. Cysteamine protection is discussed in terms of its role as an inhibitor of the toxic metabolite formation.
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PMID:Experimental acetaminophen-induced hepatic necrosis: biochemical and electron microscopic study of cysteamine protection. 10 18

The therapeutic effectiveness of bromocriptine as well as the post-operative ultrastructural aspects of treated pituitary adenomas were investigated in five acromegalic patients. Although concentrations of GH basal decreased and the glucose tolerance test and the TSH responses were significantly improved, the release of GH induced by TRH was not prevented by the dopaminergic agonist. Adenomatous cells were densely granulated and contained a dilated endoplasmic reticulum. Misplaced exocytosis was frequently observed. These findings clearly indicate that bromocriptine inhibits the spontaneous release of GH but does not interfere with the abnormal GH response to TRH. This suggests a separate site of action. The drug seems not to block the synthesizing activity of the adenomatous cell, a finding in accordance with clinical observations that warns against its use as a single therapeutic agent.
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PMID:Serum growth hormone and ultrastructural studies of adenohypophysial tissue in bromocriptine treated acromegalic patients. 10 68

Ultrastructural localization of glucose 6-phosphatase activity was studied in the tracheal epithelium of the rat. The reaction product for the enzyme activity was localized in the endoplasmic reticulum and nuclear envelope of all cell types composing the tracheal epithelium, namely ciliated cells, goblet cells, brush cells and basal cells. This pattern of localization is similar to that shown by hepatocytes, proximal convoluted tubule cells of the kidney and a variety of other cell types. The function of this enzyme in tracheal epithelial cells is discussed.
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PMID:Ultrastructural localization of glucose 6-phosphatase activity in tracheal epithelium of the rat. 16 68

The effect of temperature on the core structure of endoplasmic reticulum membranes has been visualized directly in cells of the poikilothermic eukaryote Tetrahymena pyriformis by freeze-etch electron microscopy. Moreover, the effect of temperature on the smooth microsomal membrane vesicles isolated from these cells, as well as on the extracted membrane lipids, has been examined by fluorescence probing, electron spin resonance, proton nuclear magnetic resonance, and calorimetry. Freeze-etch electron microscopy of T. pyriformis cells, equilibrated at different temperatures between 28 and 5 degrees, reveals the emergence of smooth areas on the fracture faces of endoplasmic reticulum membranes at temperatures below similar to 17 degrees. In this temperature range, we also find discontinuities in the glucose 6-phosphatase activity, in the fluorescence intensity of 8-anilino-1-naphthalensulfonate, in the partition of 4-doxyldecane, and in the separation of the outer hyperfine extrema of 5-doxylstearic acid in the microsomal membranes. These membranes apparently contain at least two lipid environments of different fluidity as indicated by the 12-doxylstearic acid spin-label. Proton nuclear magnetic resonance of the extracted membrane lipids indicates an abrupt change of the fatty acid chain mobilities at temperatures below similar to 17 degrees. This, however, is not due to a true thermal liquid crystalline in equilibrium crystalline phase transition. Calorimetric measurements also support this conclusion. The thermotropic alterations observed within the membranes are interpreted to be due primarily to a clustering of "rigid" liquid crystalline lipid environments which exclude membrane-intercalating proteins.
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PMID:Thermotropic lipid clustering in tetrahymena membranes. 16 83


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