scholarly journals Biosynthesis of lipoprotein: location of nascent apoAI and apoB in the rough endoplasmic reticulum of chicken hepatocytes

1992 ◽  
Vol 117 (6) ◽  
pp. 1161-1169 ◽  
Author(s):  
JL Dixon ◽  
R Chattapadhyay ◽  
T Huima ◽  
CM Redman ◽  
D Banerjee
Keyword(s):  
Endoplasmic Reticulum ◽  
Rough Endoplasmic Reticulum ◽  
Microscopic Examination ◽  
Microsomal Membrane ◽  
Golgi Cell ◽  
Lipoprotein Particles ◽  
Morphological Findings ◽  
Cytoplasmic Surface ◽  
Luminal Side ◽  
Cell Fractions

Our previous studies showed that in hepatic RER of young chickens, nascent apoAI is not associated with lipoprotein particles and only becomes part of these lipoprotein structures in the Golgi. In this study, we have used three different methodologies to determine the locations of apoAI and apoB in the RER and compared them to that of albumin. Immunoelectron microscopic examination of the RER cell fractions showed that both apoAI and apoB were associated only with the RER membrane whereas albumin was located both within the lumen and on the limiting membrane of the vesicles. To examine the possibility of membrane integration of nascent apoAI and apoB in the RER, we administered L-[3H]leucine to young chickens for 10 min, isolated RER, treated this cell fraction with buffers of varying pH, and measured the release of radioactive albumin, apoAI, and apoB. The majority of nascent apoAI (64%), nascent apoB (100%), and nascent albumin (97%) was released from RER vesicles at pH 11.2, suggesting that, like albumin, apolipoproteins are not integrated within the membrane. To determine if nascent apoproteins are exposed to the cytoplasmic surface, we administered L-[3H]leucine to young chickens and at various times isolated RER and Golgi cell fractions. Radioactive RER and Golgi cell fractions were treated with exogenous protease and the percent of nascent apoAI and apoB accessible to proteolysis was determined and compared to that of albumin. At 5, 10, and 20 min of labeling, 35-56% of nascent apoAI and 60-75% of apoB in RER were degraded, while albumin was refractive to this treatment. At all times both apolipoproteins and albumin present in Golgi cell fractions were protected from proteolysis. These biochemical and morphological findings indicate that apoAI and apoB are associated with the rough microsomal membrane and are partially exposed to the cytoplasmic surface at early stages of secretion. They may later enter the luminal side of the ER and, on entering the Golgi, form lipoprotein particles.

The polypeptides of rat liver nuclear envelope. II. Comparison of rat liver nuclear membrane polypeptides with those of the rough endoplasmic reticulum

1980 ◽  
Vol 43 (1) ◽  
pp. 269-277
Author(s):  
J.C. Richardson ◽  
A.H. Maddy
Keyword(s):  
Endoplasmic Reticulum ◽  
Rat Liver ◽  
Rough Endoplasmic Reticulum ◽  
Nuclear Membrane ◽  
Relative Proportion ◽  
Membrane System ◽  
Membrane Systems ◽  
Nuclear Membranes ◽  
Cytoplasmic Surface ◽  
Triton X

Nuclear envelopes are separated into pore-lamina and membrane sub-fractions by extraction in 2.0% Triton X-100 followed by pelleting of the pore-laminae. The polypeptides of these subfractions are then compared with those from isolated rough endoplasmic reticulum. The dispositions of individual polypeptides in the cytoplasmic surface of nuclear envelopes and rought endoplasmic reticulum were studied by lactoperoxidase-catalysed iodination. These studies show that although the nuclear membranes exhibit several homologies with the Triton-soluble polypeptides of the rough endoplasmic reticulum the relative proportion of individual polypeptides within the two systems are very largely different. The cytoplasmic surfaces of the 2 membrane systems show only 2 obvious homologies at 105 000 and 15 000 mol. wt and the overall impression is that, at least in rat liver, the outer nuclear membrane is very substantially differentiated from rough endoplasmic reticulum. It is concluded that the nuclear membranes may not be regarded as a mere continuum of the endoplasmic reticulum, but should be seen as a highly specialized membrane system in their own right.

scholarly journals In vivo effect of colchicine on hepatic protein synthesis and on the conversion of proalbumin to serum albumin

1978 ◽  
Vol 77 (2) ◽  
pp. 400-416 ◽  
Author(s):  
CM Redman ◽  
D Banerjee ◽  
C Manning ◽  
CY Huang ◽  
K Green
Keyword(s):  
Endoplasmic Reticulum ◽  
Protein Synthesis ◽  
Serum Albumin ◽  
Cell Fraction ◽  
Secretory Vesicles ◽  
Golgi Cell ◽  
Amino Terminal ◽  
Rna Content ◽  
Cell Fractions ◽  
Hepatic Protein Synthesis

Treatment of rats with 0.5-25 mumol/100 g body weight of colchicine for 1 h or more caused an inhibition of hepatic protein synthesis. This effect was not seen if animals were exposed to colchicine for less than 1 h. The delayed inhibition of protein synthesis affected both secretory and nonsecretory proteins. Treatment with colchicine (15 mumol/100 g) for 1 h or more caused the RNA content of membrane-bound polysomes to fall but did not change the polysomal profile of this fraction. By contrast, the total RNA content in the free polysome cell fraction was increased, and this was due to the presence of more ribosomal monomers and dimers. Electron microscope examination of the livers from rats treated for 3 h with colchicine showed an accumulation of secretory vesicles within the hepatocytes and a general distention of the endoplasmic reticulum. Administration of radioactive L-leucine to the rats led to an incorporation of radioactivity into two forms of intracellular albumin which were precipitable with antiserum to rat serum albumin but which were separable by diethylaminoethyl-cellulose chromatography. One form has arginine at the amino-terminal position and is proalbumin, and the other form, which more closely resembles serum albumin chromatographically, has glutamic acid at its amino terminus. Only proalbumin was found in rough and smooth endoplasmic reticulum fractions and in a Golgi cell fraction wich corresponds morphologically to mostly empty and partially filled secretory vesicles. However, in other Golgi cell fractions which were filled with secretory products, both radioactive proalbumin and serum albumin were found. This indicates that proalbumin is converted to serum albumin in these secretory vesicles just before exocytosis. Colchicine delayed the discharge of radioactive albumin from these filled secretory vesicles and caused an accumulation of both proalbumin and serum albumin within these cell fractions.

scholarly journals Primary fixation in osmium-potassium ferrocyanide: the staining of glycogen, glycoproteins, elastin, an intranuclear reticular structure, and intercisternal trabeculae.

1981 ◽  
Vol 29 (9) ◽  
pp. 1105-1111 ◽  
Author(s):  
S Goldfischer ◽  
Y Kress ◽  
B Coltoff-Schiller ◽  
J Berman
Keyword(s):  
Endoplasmic Reticulum ◽  
Rough Endoplasmic Reticulum ◽  
Microscopic Examination ◽  
Electron Microscopic Examination ◽  
Potassium Ferrocyanide ◽  
Nuclear Pores ◽  
Electron Microscopic ◽  
Interphase Nuclei ◽  
Reticular Structure ◽  
Cellular Components

Primary fixation in an osmium-potassium ferrocyanide (K4Fe(CN)6) mixture combines selective fixation, staining, and extraction of various cellular components; membranes, glycogen, glycoproteins, and elastin are preserved and stained. An intranuclear reticular structure that is composed of 3-6 nm fibers and permeates the entire nucleus, except for the nuclear pores, is demonstrated by electron microscopic examination of tissues prepared in an osmium-potassium ferrocyanide fixative. Condensations of the reticulum parallel the distribution of heterochromatin in interphase nuclei. This preparative procedure also reveals a network of trabeculae that are associated with the cisternae of rough endoplasmic reticulum and connect the parallel cisternae in hepatocytes, plasmacytes, neurons, and pancreatic ancinar cells. The intercisternal trabeculae are associated with both free and bound ribosomes.

scholarly journals Biosynthesis of high density lipoprotein by chicken liver: conjugation of nascent lipids with apoprotein A1.

1984 ◽  
Vol 99 (6) ◽  
pp. 1917-1926 ◽  
Author(s):  
D Banerjee ◽  
C M Redman
Keyword(s):  
Endoplasmic Reticulum ◽  
Golgi Apparatus ◽  
Smooth Endoplasmic Reticulum ◽  
Lipid Synthesis ◽  
Density Lipoprotein ◽  
Plasma Lipoproteins ◽  
Golgi Cell ◽  
Intracellular Organelles ◽  
Apoprotein A1 ◽  
Cell Fractions

To study the assembly of newly synthesized lipids with apoprotein A1, we administered [2-3H]glycerol to young chickens and determined the hepatic intracellular sites of lipid synthesis and association of nascent lipids with apoprotein A1. [2-3H]glycerol was rapidly incorporated into hepatic lipids, reaching maximal levels at 5 min, and this preceded the appearance of lipid radioactivity in the plasma. The liver was fractionated into rough and smooth endoplasmic reticulum and Golgi cell fractions. The isolated cell fractions were further subfractionated into membrane and soluble (content) fractions by treatment with 0.1 M Na2CO3, pH 11.3. At various times, the lipid radioactivity was measured in each of the intracellular organelles, in immunoprecipitable apoprotein A1, and in materials that floated at buoyant densities similar to those of plasma lipoproteins. Maximal incorporation occurred at 1 min in the rough endoplasmic reticulum, at 3-5 min in the smooth endoplasmic reticulum, and at 5 min in the Golgi cell fractions. The majority (66-93%) of radioactive glycerol was incorporated into triglycerides with smaller (4-27%) amounts into phospholipids. About 80% of the lipid radioactivity in the endoplasmic reticulum and 70% of that in the Golgi cell fractions was in the membranes. The radioactive lipids in the content subfraction were distributed in various density classes with most nascent lipids floating at a density less than or equal to 1.063 g/ml. Apoprotein A1 from the Golgi apparatus, obtained by immunoprecipitation, contained sixfold more nascent lipids than did that from the endoplasmic reticulum. These data indicate that [2-3H]glycerol is quickly incorporated into lipids of the endoplasmic reticulum and the Golgi cell fractions, that most of the nascent lipids are conjugated with apoproteins A1 in the Golgi apparatus, and that very little association of nascent lipid to apoprotein A1 occurs in the endoplasmic reticulum.

scholarly journals Transport and topology of galactosyltransferase in endomembranes of HeLa cells.

1983 ◽  
Vol 97 (3) ◽  
pp. 723-727 ◽  
Author(s):  
G J Strous ◽  
P Van Kerkhof ◽  
R Willemsen ◽  
H J Geuze ◽  
E G Berger
Keyword(s):  
Endoplasmic Reticulum ◽  
Rough Endoplasmic Reticulum ◽  
Golgi Complex ◽  
Short Pulse ◽  
Antigenic Determinants ◽  
Marker Enzyme ◽  
Uridine Diphosphate ◽  
Density Fractions ◽  
Luminal Side ◽  
Precursor Molecules

HeLa cell membranes were studied for the distribution and orientation of the Golgi marker enzyme uridine diphosphate-galactose:beta-D-N-acetylglucosamine beta, 1-4 transferase (GT). Short pulse labeling in the presence of [35S]methionine resulted in two precursor species (Mr = 44,000 and 47,000), present in a microsomal fraction with a density of 1.18 g/ml in sucrose, presumably derived from the rough endoplasmic reticulum. Processing of the N-linked oligosaccharide(s) occurred only after the precursor molecules migrated to lighter density fractions, presumably derived from the Golgi complex. The mature GT molecules (Mr = 54,000) contain O-linked oligosaccharides as shown by beta-elimination of metabolically incorporated [3H]galactose. The O-glycosylation occurred mainly in the light density fractions. The topology of GT was studied on membrane fractions after labeling with [35S]methionine as well as immunocytochemically on ultrathin cryosections at the electron microscope level. Our results indicate that both the antigenic determinants of GT as well as polypeptide chain are present intramembraneously and at the luminal side of the membranes of the Golgi complex and rough endoplasmic reticulum.

scholarly journals Alphavirus RNA replicase is located on the cytoplasmic surface of endosomes and lysosomes.

1988 ◽  
Vol 107 (6) ◽  
pp. 2075-2086 ◽  
Author(s):  
S Froshauer ◽  
J Kartenbeck ◽  
A Helenius
Keyword(s):  
Endoplasmic Reticulum ◽  
Rough Endoplasmic Reticulum ◽  
Sindbis Virus ◽  
Rna Synthesis ◽  
Viral Rna ◽  
Structural Proteins ◽  
Cytoplasmic Surface ◽  
Nucleoprotein Complexes ◽  
Secondary Lysosomes

Using morphological and cell biological techniques, we have shown that the RNA replicase of Semliki Forest and Sindbis virus (two closely related alphaviruses) is located in complex ribonucleoprotein structures associated with the cytoplasmic surface of modified secondary lysosomes and endosomes. These nucleoprotein complexes often form a bridge between the membrane of the endocytic vacuole and the rough endoplasmic reticulum where the synthesis of the structural proteins of these viruses occurs. The results suggest that these cytopathic vacuoles constitute sites not only for viral RNA synthesis, but also for translation of structural proteins, and for the assembly of nucleocapsids.

Modification of Pineal Ultrastructure by Exogenous Hormones

1967 ◽  
Vol 25 ◽  
pp. 170-171
Author(s):  
R. A. Turner ◽  
A. E. Rodin ◽  
D. K. Roberts
Keyword(s):  
Electron Microscopy ◽  
Endoplasmic Reticulum ◽  
Rough Endoplasmic Reticulum ◽  
Estradiol Benzoate ◽  
Female Rats ◽  
List Type ◽  
Type Number ◽  
Pregnant Rats ◽  
Gonadal Atrophy ◽  
Pineal Ultrastructure

There have been many reports which establish a relationship between the pineal and sexual structures, including gonadal hypertrophy after pinealectomy, and gonadal atrophy after injection of pineal homogenates or of melatonin. In order to further delineate this relationship the pineals from 5 groups of female rats were studied by electron microscopy:ControlsPregnant ratsAfter 4 weekly injections of 0.1 mg. estradiol benzoate.After 8 daily injections of 150 mcgm. melatonin (pineal hormone).After 8 daily injections of 3 mg. serotonin (melatonin precursor).No ultrastructural differences were evident between the control, and the pregnancy and melatonin groups. However, the estradiol injected animals exhibited a marked increase in the amount and size of rough endoplasmic reticulum within the pineal cells.

Membrane-associated microtubular areays induced in proximal myelinated processes of dorsal root ganglia by large doses of vitamin B6

1986 ◽  
Vol 44 ◽  
pp. 368-369
Author(s):  
V.J. Montpetit ◽  
S. Dancea ◽  
L. Tryphonas ◽  
D.F. Clapin
Keyword(s):  
Animal Model ◽  
Endoplasmic Reticulum ◽  
Dorsal Root Ganglia ◽  
Rough Endoplasmic Reticulum ◽  
Dorsal Root ◽  
Vitamin B6 ◽  
Morphological Changes ◽  
Model System ◽  
Sensory Nerves ◽  
Peripheral Sensory

Very large doses of pyridoxine (vitamin B6) are neurotoxic in humans, selectively affecting the peripheral sensory nerves. We have undertaken a study of the morphological and biochemical aspects of pyridoxine neurotoxicity in an animal model system. Early morphological changes in dorsal root ganglia (DRG) associated with pyridoxine megadoses include proliferation of neurofilaments, ribosomes, rough endoplasmic reticulum, and Golgi complexes. We present in this report evidence of the formation of unique aggregates of microtubules and membranes in the proximal processes of DRG which are induced by high levels of pyridoxine.

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