Fine Structural Localization of Acyltransferases Involved in Lipid Synthesis in Intestinal Mucosa.

1970 ◽  
Vol 28 ◽  
pp. 54-55
Author(s):  
R. J. Barrnett ◽  
J. A. Higgins
Keyword(s):  
Smooth Endoplasmic Reticulum ◽  
Lipid Synthesis ◽  
Mucosal Cell ◽  
Structural Localization ◽  
Morphological Studies ◽  
Mucosal Cells ◽  
Initial Appearance ◽  
Sh Group ◽  
Hydrolysis Of ◽  
Intestinal Mucosal Cells

The main products of intestinal hydrolysis of dietary triglycerides are free fatty acids and monoglycerides. These form micelles from which the lipids are absorbed across the mucosal cell brush border. Biochemical studies have indicated that intestinal mucosal cells possess a triglyceride synthesising system, which uses monoglyceride directly as an acylacceptor as well as the system found in other tissues in which alphaglycerophosphate is the acylacceptor. The former pathway is used preferentially for the resynthesis of triglyceride from absorbed lipid, while the latter is used mainly for phospholipid synthesis. Both lipids are incorporated into chylomicrons. Morphological studies have shown that during fat absorption there is an initial appearance of fat droplets within the cisternae of the smooth endoplasmic reticulum and that these subsequently accumulate in the golgi elements from which they are released at the lateral borders of the cell as chylomicrons.We have recently developed several methods for the fine structural localization of acyltransferases dependent on the precipitation, in an electron dense form, of CoA released during the transfer of the acyl group to an acceptor, and have now applied these methods to a study of the fine structural localization of the enzymes involved in chylomicron lipid biosynthesis. These methods are based on the reduction of ferricyanide ions by the free SH group of CoA.

Bacterial-Mucosal Cell Junctional Complexes

1974 ◽  
Vol 32 ◽  
pp. 144-145
Author(s):  
Roger C. Wagner
Keyword(s):  
Intestinal Wall ◽  
Rat Colon ◽  
Mucosal Cell ◽  
Gram Negative Bacteria ◽  
Gram Negative ◽  
Mucosal Cells ◽  
Mucosal Lining ◽  
Degenerative Alterations ◽  
Junctional Complexes ◽  
Intestinal Mucosal Cells

Bacteria exhibit the ability to adhere to the apical surfaces of intestinal mucosal cells. These attachments either precede invasion of the intestinal wall by the bacteria with accompanying inflammation and degeneration of the mucosa or represent permanent anchoring sites where the bacteria never totally penetrate the mucosal cells.Endemic gram negative bacteria were found attached to the surface of mucosal cells lining the walls of crypts in the rat colon. The bacteria did not intrude deeper than 0.5 urn into the mucosal cells and no degenerative alterations were detectable in the mucosal lining.

Demonstration of methionine synthetase in intestinal mucosal cells of the rat

1985 ◽  
Vol 69 (3) ◽  
pp. 287-292 ◽  
Author(s):  
J. N. Keating ◽  
D. G. Weir ◽  
J. M. Scott
Keyword(s):  
Crypt Cell ◽  
Cell Populations ◽  
Buffer System ◽  
Mucosal Cell ◽  
Mucosal Cells ◽  
Rat Duodenum ◽  
Small Intestinal ◽  
Intestinal Mucosal Cells ◽  
Crypt Cells

1. Methionine synthetase was measured in the mucosal cells of the rat duodenum, jejunum and ileum by a previously employed method for mucosal cell isolation. No activity was found in these cells. 2. When a dual buffer system for the isolation of villous and crypt cell population was substituted, however, methionine synthetase was found to be active in the duodenum, jejunum and ileum, both in the villous and crypt cell populations. The activity was significantly higher in the crypt cells than in the villous cells throughout the intestine, and higher levels were found in the ileum than in the duodenum or jejunum. 3. As had been previously reported for the rat liver, nitrous oxide in vivo reduced the enzyme activity in both the villous and crypt cell populations, suggesting a role in vivo for the enzyme. We conclude that methionine synthetase is both present and active in the small intestinal mucosal cells of the rat.

Hydrolysis of peptides within lumen of small intestine

1976 ◽  
Vol 231 (5) ◽  
pp. 1322-1329 ◽  
Author(s):  
DB Silk ◽  
A Nicholson ◽  
YS Kim
Keyword(s):  
Small Intestine ◽  
Brush Border ◽  
Electrophoretic Mobilities ◽  
Chemical Assay ◽  
Intestinal Contents ◽  
Mucosal Cells ◽  
Peptide Hydrolases ◽  
Hydrolysis Of ◽  
Germfree Rats ◽  
Intestinal Mucosal Cells

The quantitative significance of intraluminal peptide hydrolases in the terminal stages of peptide digestion has been investigated, and the precise origins of these enzymes have been determined. Intestinal contents and mucosae were obtained from rats anethetized with ether. Experiments carried out on pancreaticobiliary secretions and germfree rats show that pancreatic and bacterial enzymes do not contribute significantly toward the luminal digestion of dipeptides. Chemical assay data, thermostability studies, and examination of electrophoretic mobilities of luminal peptide hydrolases indicate that jejunal enzymes originate predominantly from the cytoplasm of intestinal mucosal cells, whereas the brush border of muosal cells is a major source of the enzymes in the ileum. With glycl-L-phenylalanine and L-phenylalanyl-glycine as substrates, jejunal luminal activity was less than 2.6% of mucosal activity. Brush-border peptide hydrolase activity in ileal contents, however, was 11.9% and 40.7% of mucosal brush-border activity for the two substrates. Luminal enzymes thus play an insignifcant role in the terminal digestion of peptides in the jejunum, but have a much more important role in the ileal digestion of peptides.

A Reappraisal of ‘Osmotic’ Evidence for Intact Peptide Absorption

1977 ◽  
Vol 53 (3) ◽  
pp. 241-248
Author(s):  
P. D. Fairclough ◽  
D. B. A. Silk ◽  
J. P. W. Webb ◽  
M. L. Clark ◽  
A. M. Dawson
Keyword(s):  
Water Absorption ◽  
Peptide Absorption ◽  
Perfusion Technique ◽  
Double Lumen ◽  
Mucosal Cells ◽  
Normal Human ◽  
Solute Absorption ◽  
Saline Solutions ◽  
Hydrolysis Of ◽  
Intestinal Mucosal Cells

1. The validity of evidence for intact peptide absorption, derived from analysis of the relation of water and total solute absorption, has been tested. 2. Solute and water absorption from saline solutions of the disaccharide maltose have been studied in the normal human jejunum, using a double-lumen perfusion technique with a proximal occlusive balloon. It was expected that maltose would yield very different results from peptides, because maltose is virtually completely hydrolysed before absorption, whereas a proportion at least of some peptides is transported into the intestinal mucosal cells before hydrolysis. This expectation was not confirmed by experiment. 3. The assumption that the absorbate is always isotonic with plasma has been tested by altering the osmolality of glucose/saline solutions perfused in the jejunal lumen. This assumption was not substantiated by experiment, as when the luminal fluid was hypertonic to plasma, so was the absorbate. 4. It is suggested that our findings with peptides and saccharides could be explained by the production of a hypertonic absorbate by hydrolysis of these solutes to their monomer units. We therefore conclude that analyses of the relation of net solute and water absorption cannot be used to predict the form in which peptides enter the mucosal cells.

scholarly journals FINE STRUCTURAL LOCALIZATION OF ACYLTRANSFERASES

1971 ◽  
Vol 50 (1) ◽  
pp. 102-120 ◽  
Author(s):  
Joan A. Higgins ◽  
Russell J. Barrnett
Keyword(s):  
Endoplasmic Reticulum ◽  
Lipid Droplets ◽  
Enzyme System ◽  
Smooth Endoplasmic Reticulum ◽  
Absorptive Cell ◽  
Fixed Tissue ◽  
Structural Localization ◽  
Morphological Studies ◽  
Golgi Membranes ◽  
Insoluble Precipitate

A study of the fine structural localization of the acyltransferases of the monoglyceride and α-glycerophosphate pathways for triglyceride synthesis in the intestinal absorptive cell is reported. Glutaraldehyde-fixed tissue was found to synthesize diglyceride and triglyceride from monopalmitin and palmityl CoA, and parallel morphological studies showed the appearance of lipid droplets in the smooth endoplasmic reticulum of the absorptive cell. Glutaraldehyde-fixed tissue also synthesized triglyceride from α-glycerophosphate, although this enzyme system was more susceptible to fixation than the monoglyceride pathway acyltransferases. Cytochemical methods for the localization of free CoA were based (a) on the formation of the insoluble lanthanium mercaptide of CoA and (b) on the reduction of ferricyanide by CoA to yield ferrocyanide which forms an insoluble precipitate with manganous ions. By these methods the monoglyceride pathway acyltransferases were found to be located mainly on the inner surface of the smooth endoplasmic reticulum. The α-glycerophosphate pathway acyltransferases were localized mainly on the rough endoplasmic reticulum. Activity limited to the outer cisternae of the Golgi membranes occurred with both pathways. The possible organization of triglyceride absorption and chylomicron synthesis is discussed in view of these results.

In vitro Action of Gastric Mucosal Lysosomal Enzymes on Intracellular Gastric Glycoproteins

1979 ◽  
Vol 34 (1-2) ◽  
pp. 90-95 ◽  
Author(s):  
Fouad M. Fouad ◽  
D. Waldron-Edward
Keyword(s):  
Cell Wall ◽  
Lysosomal Enzymes ◽  
Gastric Ulceration ◽  
Mucosal Cell ◽  
Gastric Lesions ◽  
Acid Hydrolases ◽  
Gastric Mucosal Cells ◽  
Mucosal Cells ◽  
Specific Increase

Abstract The results show that incubation of gastric mucosal cells from rat at pH ~4.5 or in the presence of aspirin is associated with a specific increase in the activity of some acid-hydrolases. Intracellular glycoproteins, isolated by non-degradative techniques from rat or dog fundic mucosal cells, were found to be potential bio-substrates for these acid-hydrolyses. This may suggest that cleavage of the carbohydrate moieties of the intracellular and mucosal cell wall glycoproteins is a fundamental step in the development of gastric ulceration. A model for gastric lesions is proposed and discussed in the light of the results obtained.

scholarly journals The Platelet Dense Tubular System: Its Relationship of Prostaglandin Synthesis and Calcium Flux

1977 ◽  
Author(s):  
Jonathan M. Gerrard ◽  
James G. White
Keyword(s):  
Smooth Endoplasmic Reticulum ◽  
Divalent Cations ◽  
Lipid Synthesis ◽  
Prostaglandin Synthesis ◽  
Calcium Flux ◽  
Secretory Cells ◽  
Ultrastructural Studies ◽  
Tubular System ◽  
Relationship Of ◽  
Columnar Cells

Evidence that the dense tubular system (DTS) is the site of platelet prostaglandin synthesis derives from several observations. First platelet peroxidase is localized in the DTS. Aminotriazole which inhibits the platelet peroxidase, inhibits prostaglandin biosynthesis at the same concentration. Secondly, a similar peroxidase occurs in the secretory cells of the sheep vesicular gland (SVG) and other cells known to be involved in prostaglandin synthesis. Third, the DTS is smooth endoplasmic reticulum (SER) and SER, which is abundant in the prostaglandin synthesizing columnar cells of the SVG secretory units, is known to be involved in lipid synthesis and metabolism in other tissues. Evidence that calcium is stored in the DTS derives from ultrastructural studies showing that the DTS is analagous to the sarcotubules of skeletal muscle, and that the DTS has the capacity to bind divalent cations. Evidence that calcium flux and prostaglandin synthesis are closely linked comes from several observations which suggest 1) that movement of calcium ions to the site where arachidonic acid (AA) is released from the precursor phospholipids to be used for synthesis of prostaglandins, stimulates the AA release and 2) that synthesized prostaglandin G2, prostaglandin H2, and/or thromboxane A2 initiate platelet contraction by moving calcium from the site of synthesis to the vicinity of the contractile actin and myosin. The results suggest that the DTS, prostaglandin and thromboxane synthesis, and calcium flux are integral parts of the system modulating platelet activation.

scholarly journals Major Histocompatibility Complex Class II Inhibits Fas Antigen-Mediated Gastric Mucosal Cell Apoptosis through Actin-Dependent Inhibition of Receptor Aggregation

2005 ◽  
Vol 73 (10) ◽  
pp. 6311-6321 ◽  
Author(s):  
Calin Stoicov ◽  
Xun Cai ◽  
Hanchen Li ◽  
Kristine Klucevsek ◽  
Jane Carlson ◽  
...  
Keyword(s):  
Helicobacter Pylori ◽  
Major Histocompatibility Complex ◽  
Major Histocompatibility Complex Class ◽  
Mucosal Cell ◽  
Complex Class ◽  
Gastric Mucosal Cells ◽  
Fas Antigen ◽  
Histocompatibility Complex ◽  
Receptor Aggregation ◽  
Mucosal Cells

ABSTRACT Escape from normal apoptotic controls is thought to be essential for the development of cancer. During Helicobacter pylori infection, the leading cause of gastric cancer, activation of the Fas antigen (Fas Ag) apoptotic pathway is responsible for early atrophy and tissue loss. As disease progresses, metaplastic and dysplastic glands arise which express Fas Ag but are resistant to apoptosis and are believed to be the precursor cells for adenocarcinoma. In this report, we show that one mechanism of acquired Fas resistance is inhibition of receptor aggregation via a major histocompatibility complex class II (MHCII)-mediated, actin-dependent mechanism. For these studies we used the well-described C57BL/6 mouse model of Helicobacter pylori and Helicobacter felis infection. Under normal conditions, Fas Ag is expressed at low levels, and MHCII expression on gastric mucosal cells is negligible. With infection and inflammation, both receptors are upregulated, and 6.1% of gastric mucosal cells express MHCII in combination with Fas Ag. Using the rat gastric mucosal cell line RGM-1 transfected with murine Fas Ag and MHCIIαβ chains, we demonstrate that MHCII prevents Fas receptor aggregation and inhibits Fas-mediated signaling through its effects on the actin cytoskeleton. Depolymerization of actin with cytochalasin D allows receptors to aggregate and restores Fas sensitivity. These findings offer one mechanism by which gastric mucosal cells acquire Fas resistance.

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