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Query: HUMANGGP:036206 (endoplasmic reticulum)
 63,868 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

As has been known for several years, thoroughly purified ribosomes contain a firmly bound serine proteinase with an optimum of activity at neutral pH. The present paper shows that the activity is found in free cytoplasmic ribosomes as well as in ribosomes detached from the membranes of the endoplasmic reticulum of rat liver. After ribosome dissociation, the proteinase activity is found only on the 40 S subunits. Recovery of the proteinase in the proteins of whole ribosomes or of 40 S subunits amounts to 44 and 65%, respectively. Ribosomes purified both from plant (Euglena) and bacterial (Acinetobacter) cells contain a serine proteinase having an activity quite comparable to that of rat liver ribosomes. In view of the recommendations of BARRETT et al. ( in REICH, RIFKIN and SHAW (eds).: Proteinases and Biological Control, Cold Spring Harbour Lab., 1975, p. 481), who no longer restrict the name "cathepsin" to acid or even lysosomal proteinases, we propose the name " ccathepsin R" for this ribosomal serine proteinase.
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PMID:The ribosomal serine proteinase: cathepsin R. 4 62

This report describes morphological and biochemical changes accompanying oestrogen induced synthesis of the egg-yolk protein precursor, vitellogenin, in male Xenopus liver. Extensive proliferation of the rough and smooth endoplasmic reticulum and the Golgi apparatus occurs between 3 and 9 days after administration of oestradiol-17 beta. Subcellular fractionation showed that microsomal fractions have an increased number of ribosomes available for protein synthesis, hormone treatment enhances the in vitro protein synthetic capacity per unit of RNA; both in microsome and ribosome preparations. Polypeptides synthesized in vitro by ribosome preparations show an enrichment in serine content after hormone treatment and an increased proportion of ribosomes can be immunoprecipitated by antibodies directed against vitellogenin. Our data are consistent with the proposal that vitellogenin is synthesized on the ribosomes of the rough endoplasmic reticulum and processed and packaged for secretion in the smooth endoplasmic reticulum and Golgi apparatus. Response to hormonal induction of vitellogenin involves an early phase in which membrane proliferation occurs in order to increase the cellular capacity to synthesize, process and secrete large quantities of egg-yolk protein precursor.
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PMID:Morphological and biochemical changes in the hepatic endoplasmic reticulum and golgi apparatus of male Xenopus laevis after induction of egg-yolk protein synthesis by oestradiol-17 beta. 18 Dec 82

The testicular interstitial cell of the bat, Myotis schreibersi (Temmink), captured late in August was electron microscopically investigated. The cytoplasm of Myotis interstitial cells is packed by strikingly numerous mitochondria with many electron dense small matrix granules, endoplasmic reticulum and variable numbers of osmiophilic lipid droplets. The Myotis interstitial cell is characterized by alternate development of the SER and RER: In some Leydig cells the major part of the cytoplasm is packed by tubular SER, whereas in others this apparently is replaced by abundant free ribosomes containing sparse cisternae of the RER. These changes in the amounts of ser and RER are likely reversible and probably reflect functional alterations of Leydig cells of the bat, a hibernator. The Myotis interstitial cell possesses small cytoplasmic crystalloids composed of regularly oriented, compressed tubules, 20-28 m mu thick, which are continuous to the tubular SER (SER derived crystalloids). Type I and type II crystalloids are classified, which show, in suitable planes of section, honeycomb-like and fabric-like patterns, respectively. The Myotis Leydig cell extends cytoplasmic processes of irregular shape and long microvilli, the latter often conglomerates on the cell body or cytoplasmic processes. The entire surface of the cell including the processes is completely surrounded by a basal lamina.
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PMID:Electron microscope study on the bat testicular interstitial cell with special reference to the cytoplasmic crystalloid. 22 15

Epithelial glycoprotein like that produced by the gastric surface consists of a polypeptide chain rich in serine and threonine; to these amino acid residues oligosaccharide chains of variable length are linked. The linking sugar is acetylgalactosamine. To find out whether the initial glycosylation takes place at the ribosomal level. I treated purified peptidyl-tRNA, derived from rat gastric membrane-bound polysomes, with alkali in the presence of boro[3H]hydride. Alkali specifically splits glycosidic bonds between serine or threonine and oligosaccharide side chains (beta-elimination reaction). The linking sugar is converted to an alditol and simultaneously labeled. GalNAc was identified as the linking sugar by paper chromatography. Furthermore, nascent peptides with lengths between 40 and 60 amino acid residues already contained this linking sugar. Gel filtration on Bio-Gel P-2 of 3H-labeled saccharides revealed that nascent chains contained mainly monosaccharides, but some di- or trisaccharides were found with GalNAc as the linkage sugar. These findings demonstrate that initial glycosylation of epithelial glycoprotein occurs at the ribosomal level rather shortly after the nascent peptide chain has reached the cisternal lumen of the endoplasmic reticulum.
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PMID:Initial glycosylation of proteins with acetylgalactosaminylserine linkages. 28 57

The use of L-[35S]methionine (500-700 Ci/mmol (1 Ci = 37 GBq) for labelling the polypeptides of liver rough (R) and smooth (S)endoplasmic reticulum (ER) membrane fractions in vivo was studied. Adult mice were injected intraperitoneally with 400 muCi of the isotope and killed at various times (2'min to 24 h) thereafter. RER and SER fractions were prepared, stripped of ribosomes, and treated with Triton X-100 to remove intravesicular contents. Sufficient radioactivity was present in individual aliquots (75 microgram protein) of the ER membrane fractions to permit their analysis by fluorography after separation by electrophoresis in polyacrylamide gels containing sodium dodecyl sulphate. By 3 min, although the majority of the labelled components were of intravesicular origin, some 12 membrane polypeptides were labelled in the RER fraction (including one corresponding in migration to cytochrome P-450); some 6 of these latter polypeptides were labelled to a lesser degree in the SER membrane fraction at this time. By 5 min, the patterns of radioactive polypeptides of the RER and SER fractions (including both membrane and intravesicular components) were identical. By 7 min, some 28 labelled membrane polypeptides were detectable in the total microsomal membrane. Analysis of the 24-h samples revealed that all the membrane polypeptides seen by staining with Coomassie blue were visualised by fluorography. Other studies revealed the applicability of the approach used for producing highly labelled cell sap and serum proteins. The overall results demonstrate the suitability of L-[35S]methionine administered in vivo for producing mouse liver ER membrane polypeptides of relatively high radioactivity and are consistent with a rapid conversion of RER to SER by ribosome detachment or membrane flow.
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PMID:Suitability of L-[35S]methionine for studying the biosynthesis of the polypeptides of mouse liver endoplasmic reticulum membrane fractions in vivo. 47 10

Metallic cobalt and aluminum rods were implanted into the cerebral cortices of rats. Almost all the animals with cobalt implantation were found to be epileptic 30 days after the operation. Tissue samples from the cerebral cortices were sampled for electron microscopy. The most significant changes in the cobalt-implanted animals were the disintegration of the rough endoplasmic reticulum in many cortical neurons and the accumulation of neurofilaments within the perikaryon. Such filamentous accumulation was usually found near the perinuclear position, at the periphery of the neurons, and in areas where there was a paucity of regular rough endoplasmic reticulum. Large aggregates of SER-like tubulovesicular structures were also found within many neuronal processes. Some of these neuronal processes could be identified to be postsynaptic dendritic terminals. Large nuclear pseudo-inclusions consisting of cytoplasmic materials were also found in some cortical neurons. These ultrastructural changes could also be occasionally observed in the opposite (cobalt-free) hemisphere of the brain (mirror image) in the cobalt-implanted animals. However, the brains of the aluminum-implanted or blank-control animals were free from any of these changes.
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PMID:Cobalt-induced epilepsy: an ultrastructural study. 57 56

Electron microscopic observations on normally differentiating and alpha-MSH (melanocyte-stimulating hormone)-treated epidermal melanocytes of newborn mouse skin were carried out. The process of melanocyte differentiation from premelanosome-containing melanoblasts was investigated in detail with respect to melanosomes as markers. Melanoblasts containing unmelanized premelanosomes gradually decreased in number after birth, while the number of melanocytes rapidly increased. The epidermis of alpha-MSH-treated 3-day-old mice and normal 6-day-old mice contained melanocytes with numerous fully melanized melanosomes, and with no or only a few melanoblasts. Changes in other organelles in differentiating melanocytes were also noticeable. Golgi apparatus and RER (rough endoplasmic reticulum) decreased in number during the normal or alpha-MSH-induced differentiation of the epidermal melanocytes, though the number of mitochondria showed no notable change. The number of SER (smooth endoplasmic reticulum) per cell did not change in the cells of newborn mice, while in alpha-MSH-treated cells the number increased significantly. These results led us to an assumption that Golgi apparatus or RER transforms into other forms of organelles including melanosomes and SER during the differentiation of melanocytes.
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PMID:Changes of organelles associated with the differentiation of epidermal melanocytes in the mouse. 63 32

1. Methionine adenosyltransferase (ATP:L-methionine-S-adenosyl transferase, EC 2.5.1.6), cystathionine beta-synthase F1L-serine hydro-lyase (adding homocysteine), EC 4.2.1.22] and cystathionine gamma-lyase [L-cystathionine cysteine-lyase (deaminating), EC 4.4.1.1] activities were found only in the cytosol fraction of rat liver cells. None was found in the mitochondrial or endoplasmic reticulum fractions as judged by the distribution of marker enzymes on a density gradient after centrifugation of the cytoplasmic fraction of a liver homogenate, or in a preparation of liver cell nuclei. 2. Polymorphs, lymphocytes (with admixed monocytes) and mixed bone marrow white cells contained no methionine adenosyl transferase, cystathionine beta-synthase or cystathionine gamma-lyase activities. 3. The possible bearing of these results on the problem of abnormal cystine storage in cystinosis is briefly discussed.
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PMID:Methionine adenosyltransferase, cystathionine beta-synthase and cystathionine gamma-lyase activity of rat liver subcellular particles, human blood cells and mixed white cells from rat bone marrow. 105 81

Ultrastructurally, the adrenal cortex of the Mongolian gerbil can be divided into two main regions and one narrow interposed border zone. The outer region corresponds to the zona glomerulosa and zona fasciculata of the rat adrenal cortex, whereas the inner region corresponds to the rat zona reticularis. The mitochondria are variable in shape, size and internal structure but generally lamelliform or tubulo-vesicular with a dense matrix in the outer region and plate-like and tubular in the inner region. Some of the mitochondria in the border region are of the polylaminar membranous type. The endoplasmic reticulum is abundant and smooth in the outer region but less prominent in the inner regions, where it is both smooth and rough. The concentric whorled membranes of rough endoplasmic reticulum are a characteristic feature of the border zone. Lipid vacuoles are abundant in the outer region. Lysosomes are numerous in the inner region and tend to form groups of 4 or 5. Aminoglutethimide causes a less conspicuous alteration in the adrenal cortex of the Mongolian gerbil than in the rat. The main alterations consist of a profound increase of lipid and lysosomes, a decrease in the number of SER profiles, and complete disappearance of the whorled membranes of RER.
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PMID:The ultrastructure of the adrenal cortex of the Mongolian gerbil (M. unguiculatus). 118 55

Serine palmitoyltransferase, 3-dehydrosphinganine reductase and sphinganine N-acyltransferase are responsible for the first steps in sphingolipid biosynthesis forming 3-oxosphinganine, sphinganine, and dihydroceramide, respectively. We confirmed the localization of these enzymes in the endoplasmic reticulum (ER) using highly purified mouse liver ER and Golgi preparations. Mild digestion of sealed "right-side out" mouse liver ER derived vesicles with different proteolytic enzymes under conditions where latency of mannose-6-phosphatase was 90% produced approximately 60-80% inactivation of serine palmitoyltransferase, 3-dehydrosphinganine reductase, and sphinganine N-acyltransferase activities. These sphingolipid biosynthetic activities (serine palmitoyltransferase, 3-dehydrosphinganine reductase, and sphinganine N-acyltransferase) are not latent, indicating that they face the cytosolic side of the ER, so that substrates have free access to their active sites. Moreover, the membrane-impermeable compound, 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid, which binds to a large number of ER proteins, inhibits serine palmitoyltransferase and sphinganine N-acyltransferase activities by 30-70%.
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PMID:Subcellular localization and membrane topology of serine palmitoyltransferase, 3-dehydrosphinganine reductase, and sphinganine N-acyltransferase in mouse liver. 131 56


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