scholarly journals Cholesterol and Steroid Synthesizing Smooth Endoplasmic Reticulum of Adrenocortical Cells Contains High Levels of Proteins Associated with the Translocation Channel

Endocrinology ◽  
2005 ◽  
Vol 146 (10) ◽  
pp. 4234-4249 ◽  
Author(s):  
Virginia H. Black ◽  
Archana Sanjay ◽  
Klaus van Leyen ◽  
Brett Lauring ◽  
Gert Kreibich
Keyword(s):  
Endoplasmic Reticulum ◽  
Rough Endoplasmic Reticulum ◽  
Smooth Endoplasmic Reticulum ◽  
Steroid Metabolism ◽  
Adrenocortical Cells ◽  
Steroid Synthesis ◽  
Local Synthesis ◽  
Peptide Cleavage ◽  
Cotranslational Translocation ◽  
Tubular Endoplasmic Reticulum

Steroid-secreting cells are characterized by abundant smooth endoplasmic reticulum whose membranes contain many enzymes involved in sterol and steroid synthesis. Yet they have relatively little morphologically identifiable rough endoplasmic reticulum, presumably required for synthesis and maintenance of the smooth membranes. In this study, we demonstrate that adrenal smooth microsomal subfractions enriched in smooth endoplasmic reticulum membranes contain high levels of translocation apparatus and oligosaccharyltransferase complex proteins, previously thought confined to rough endoplasmic reticulum. We further demonstrate that these smooth microsomal subfractions are capable of effecting cotranslational translocation, signal peptide cleavage, and N-glycosylation of newly synthesized polypeptides. This shifts the paradigm for distinction between smooth and rough endoplasmic reticulum. Confocal microscopy revealed the proteins to be distributed throughout the abundant tubular endoplasmic reticulum in these cells, which is predominantly smooth surfaced. We hypothesize that the broadly distributed translocon and oligosaccharyltransferase proteins participate in local synthesis and/or quality control of membrane proteins involved in cholesterol and steroid metabolism in a sterol-dependent and hormonally regulated manner.

THE ULTRASTRUCTURE OF THE HUMAN GRANULOSAL LUTEIN CELL OF THE FIRST TRIMESTER OF GESTATION

1968 ◽  
Vol 58 (3) ◽  
pp. 481-496 ◽  
Author(s):  
Poul Hjortkjær Pedersen ◽  
Jørgen Falck Larsen
Keyword(s):  
Endoplasmic Reticulum ◽  
Smooth Endoplasmic Reticulum ◽  
First Trimester ◽  
Corpora Lutea ◽  
Steroid Synthesis ◽  
Intracellular Location ◽  
Human Pregnancy ◽  
Subendothelial Space ◽  
Lutein Cell ◽  
Early Human

ABSTRACT The ultrastructure of granulosal lutein cells of 13 corpora lutea in early human pregnancy was studied. The predominant cytoplasmic element was the smooth endoplasmic reticulum. No convincing signs of degeneration of the lutein cells could be demonstrated within the first 14 weeks of pregnancy, as the mitochondria as well as the rough and smooth endoplasmic reticulum were well preserved. However, lysosomes may be slightly more numerous in older specimens and the subendothelial space increases with the age of gestation. A particular type of multilaminated structure one to five micron in diameter was observed, particularly in the earliest specimens. The possible intracellular location of steroid synthesis is discussed.

scholarly journals Glycosyltransferase activities in Golgi complex and endoplasmic reticulum fractions isolated from African trypanosomes.

1984 ◽  
Vol 99 (2) ◽  
pp. 569-577 ◽  
Author(s):  
D J Grab ◽  
S Ito ◽  
U A Kara ◽  
L Rovis
Keyword(s):  
Endoplasmic Reticulum ◽  
Rough Endoplasmic Reticulum ◽  
Golgi Complex ◽  
Smooth Endoplasmic Reticulum ◽  
Surface Glycoprotein ◽  
Relative Distribution ◽  
African Trypanosomes ◽  
Independent Form ◽  
Variable Surface ◽  
Dependent Form

Highly enriched Golgi complex and endoplasmic reticulum fractions were isolated from total microsomes obtained from Trypanosoma brucei, Trypanosoma congolense, and Trypanosoma vivax, and tested for glycosyltransferase activity. Purity of the fractions was assessed by electron microscopy as well as by biochemical analysis. The relative distribution of all the glycosyltransferases was remarkably similar for the three species of African trypanosomes studied. The Golgi complex fraction contained most of the galactosyltransferase activity followed by the smooth and rough endoplasmic reticulum fractions. The dolichol-dependent mannosyltransferase activities were highest for the rough endoplasmic reticulum, lower for the smooth endoplasmic reticulum, and lowest for the Golgi complex. Although the dolichol-independent form of N-acetylglucosaminyltransferase was essentially similar in all the fractions, the dolichol-dependent form of this enzyme was much higher in the endoplasmic reticulum fractions than in the Golgi complex fraction. Inhibition of this latter activity in the smooth endoplasmic reticulum fraction by tunicamycin A1 suggests that core glycosylation of the variable surface glycoprotein may occur in this organelle and not in the rough endoplasmic reticulum as previously assumed.

scholarly journals The disulphide-bonded nature of procollagen and the role of the extension peptides in the assembly of the molecule

1977 ◽  
Vol 161 (2) ◽  
pp. 405-418 ◽  
Author(s):  
R Harwood ◽  
A H Merry ◽  
D E Woolley ◽  
M E Grant ◽  
D S Jackson
Keyword(s):  
Endoplasmic Reticulum ◽  
Rough Endoplasmic Reticulum ◽  
Smooth Endoplasmic Reticulum ◽  
Gel Filtration ◽  
Close Correlation ◽  
Helical Conformation ◽  
Composite Gels ◽  
Tendon Cells ◽  
Cartilage Cells ◽  
And Cartilage

1. The molecular weights of chick tendon and cartilage procollagens, and their constituent polypeptides, were determined by gel filtration and gel electrophoresis. The values obtained are in good agreement and indicate that the mol.wts. of the secreted procollagens (types I and II) and their individual pro-alpha-chains are of the order of 405 000-445 000 and 137 000-145 000 respectively.2. Digestion of tendon procollagen with human rheumatoid synovial collagenase gave products consistent with the presence of large non-helical peptide extensions at both N-and C-termini. Electrophoretic analysis gave apparent mol.wts. of 17 500 and 36 000 for the respective N- and C-terminal extensions of pro-alpha1(I)-and pro-alpha2-chains, and inter-chain disulphide bonds were restricted to the C-terminal location. 3. During the biosynthesis of procollagen by tendon and cartilage cells a close correlation was observed between the extent of inter-chain disulphide bonding and the proportion of procollagen polypeptides having a triple-helical conformation. These processes appeared to commence in the rough endoplasmic reticulum and be completed in the smooth endoplasmic reticulum, but the rate at which they occur in cartilage cells is markedly slower than that found in tendon cells. 4. When the intracellular [14C]procollagen polypeptides present in the rough-endoplasmic-reticulum fractions of tendon and cartilage cells were analysed under non-reducing conditions on agarose/polyacrylamide composite gels, no significant pools of dimeric intermediates were detected. 5. In both cell types, inter-chain disulphide-bond formation occurred even when hydroxylation, and hence triple-helix formation, was inhibited. The presence of pro-alpha1- and pro-alpha2-components in a ratio of 2:1 in the disulphide-linked unhydroxylated procollagen isolated from tendon cells demonstrated that correct chain association occurs in the absence of hydroxylation. This observation is consistent with a model for the assembly of pro-gamma112-chains in which the recognition and selection of pro-alpha1-and pro-alpha2-chains in a 2:1 ratio are directed by the non-helical C-terminal extension peptides of tendon procollagen.

scholarly journals DIFFERENTIATION OF ENDOPLASMIC RETICULUM IN HEPATOCYTES

1971 ◽  
Vol 49 (2) ◽  
pp. 264-287 ◽  
Author(s):  
A. Leskes ◽  
P. Siekevitz ◽  
G. E. Palade
Keyword(s):  
Endoplasmic Reticulum ◽  
Phosphatase Activity ◽  
Rough Endoplasmic Reticulum ◽  
Specific Activity ◽  
Smooth Endoplasmic Reticulum ◽  
Rat Hepatocytes ◽  
Adult Level ◽  
Enzyme Specific Activity ◽  
Cytochemical Reaction ◽  
And Control

The distribution of glucose-6-phosphatase activity in rat hepatocytes during a period of rapid endoplasmic reticulum differentiation (4 days before birth-1 day after birth) was studied by electron microscope cytochemistry. Techniques were devised to insure adequate morphological preservation, retain glucose-6-phosphatase activity, and control some other possible artifacts. At all stages examined the lead phosphate deposited by the cytochemical reaction is localized to the endoplasmic reticulum and the nuclear envelope. At 4 days before birth, when the enzyme specific activity is only a few per cent of the adult level, the lead deposit is present in only a few hepatocytes. In these cells a light deposit is seen throughout the entire rough-surfaced endoplasmic reticulum. At birth, when the specific activity of glucose-6-phosphatase is approximately equal to that of the adult, nearly all cells show a positive reaction for the enzyme and, again, the deposit is evenly distributed throughout the entire endoplasmic reticulum. By 24 hr postparturition all of the rough endoplasmic reticulum, and in addition the newly formed smooth endoplasmic reticulum, contains heavy lead deposits; enzyme activity at this stage is 250% of the adult level. These findings indicate that glucose-6-phosphatase develops simultaneously within all of the rough endoplasmic reticulum membranes of a given cell, although asynchronously in the hepatocyte population as a whole. In addition, the enzyme appears throughout the entire smooth endoplasmic reticulum as the membranes form during the first 24 hr after birth. The results suggest a lack of differentiation within the endoplasmic reticulum with respect to the distribution of glucose-6-phosphatase at the present level of resolution.

Biogenesis of Smooth Endoplasmic Reticulum in Hepatocytes of Phenobarbital Treated Rats

1974 ◽  
Vol 32 ◽  
pp. 308-309
Author(s):  
Joan A. Higgins
Keyword(s):  
Endoplasmic Reticulum ◽  
Rough Endoplasmic Reticulum ◽  
Specific Activity ◽  
Smooth Endoplasmic Reticulum ◽  
Rat Hepatocytes ◽  
Membrane Formation ◽  
Drug Detoxification ◽  
Marked Proliferation

In response to intraperitoneal injections of phenobarbital there is a marked proliferation of smooth endoplasmic reticulum membranes (s.e.r.) of rat hepatocytes, with little change in other membranous organelles. This increased membrane formation is accompanied by a rise in the specific activity of the enzymes involved in drug detoxification initially in the rough endoplasmic reticulum (r.e.r.) followed by a rise in the s.e.r. There is also an increased accumulation of glycerophospholipid in the newly formed s.e.r.

scholarly journals Polyribosomal attachment to rat liver and hepatoma endoplasmic reticulum in vitro. A method for its study

1971 ◽  
Vol 121 (2) ◽  
pp. 271-278 ◽  
Author(s):  
W. L. Ragland ◽  
T. K. Shires ◽  
H. C. Pitot
Keyword(s):  
Endoplasmic Reticulum ◽  
Electron Microscope ◽  
Citric Acid ◽  
Low Temperature ◽  
Rough Endoplasmic Reticulum ◽  
Half Life ◽  
Binding Capacity ◽  
Smooth Endoplasmic Reticulum ◽  
Quantitative Separation

A system for study and measurement of the attachment in vitro of exogenous polyribosomes to membranes has been presented. Its main features are use of low temperature, post-microsomal supernatant, pyrophosphate and citric acid to remove ribosomes from the surface of rough endoplasmic reticulum, and a method for quantitative separation of unattached from membrane-associated polyribosomes. The following were found. (1) Rough endoplasmic reticulum, from which ribosomes had been removed by treatment with pyrophosphate and citrate, bound over 50% of added polyribosomes, whereas the untreated (or control) rough and smooth endoplasmic reticulum and the smooth endoplasmic reticulum treated with pyrophosphate–citrate did not bind polyribosomes. (2) The polyribosome-binding capacity of rough endoplasmic reticulum stripped of its ribosomes decayed upon storage of the membranes at 0–4°C. The half-life of this decay was about 6 days whereas that of the polyribosome-binding capacity of hepatoma stripped rough endoplasmic reticulum was about 1.5 days. (3) Preparations of stripped rough endoplasmic reticulum after reassociation with polyribosomes in vitro were quite similar to preparations of native rough endoplasmic reticulum as viewed with the electron microscope. Evidence is presented to support the contention that association of polyribosomes with membranes was the result of polyribosomal reattachment to the membranes rather than trapping of the polyribosomes between vesicles of the membranes.

Anisopachous Cisternae and Cubic Lattice Structures in Hepatocytes of Rats Treated with Aminotriazole

1974 ◽  
Vol 32 ◽  
pp. 200-201
Author(s):  
Z. Hruban ◽  
A. Slesers ◽  
M. Gotoh
Keyword(s):  
Endoplasmic Reticulum ◽  
Smooth Endoplasmic Reticulum ◽  
Young Male ◽  
Chow Diet ◽  
Sprague Dawley ◽  
Metabolizing Enzymes ◽  
Cubic Lattice ◽  
Sprague Dawley Rats ◽  
Tubular Endoplasmic Reticulum ◽  
Stimulation Of

Administration of 3-amino-l,2,4-triazole (AT) decreases the activities of drug-metabolizing enzymes and inhibits the stimulation of the drugmetabolizing activities by the administration of phenobarbital (1). In the present study 1% AT in chow diet was fed ad libitum to young male Sprague-Dawley rats for 6 weeks. Thyroxin was given at 0, 0.5, 1.0, 1.5 and 2.0 ng per liter of drinking water. It was established that 1.0 mg thyroxin/L is adequate to prevent thyromegaly induced by AT.Rats fed AT alone or with 0.5% acetylsalicylic acid for 6 weeks showed alterations of the endoplasmic reticulum in their liver cells. The hepatocytes contained variable amounts of conglomerates of the tubular smooth endoplasmic reticulum (Figs. 8, 9), some of which were less than 0.5 micron in diameter (Figs. 5, 6). The anastomosing tubules were more closely packed and the intertubular spaces were narrower when compared with tubular endoplasmic reticulum of normal hepatocytes.

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