scholarly journals Carrier-mediated transport of intact UDP-glucuronic acid into the lumen of endoplasmic-reticulum-derived vesicles from rat liver

1994 ◽  
Vol 302 (1) ◽  
pp. 261-269 ◽  
Author(s):  
X Bossuyt ◽  
N Blanckaert
Keyword(s):  
Endoplasmic Reticulum ◽  
Rat Liver ◽  
Glucuronic Acid ◽  
Double Labelling ◽  
Carrier Mediated Transport ◽  
Cytosolic Side ◽  
Stimulation Experiments ◽  
Uptake Studies ◽  
Rapid Hydrolysis ◽  
Hydrolysis Of

Uptake and metabolism of UDP-glucuronic acid (UDPGlcA) by rough-endoplasmic-reticulum (RER)-derived vesicles was studied. Analysis of the molecular species, double-labelling experiments and trans-stimulation experiments revealed that initial uptake represented entry into microsomes of predominantly intact UDPGlcA, concomitant with rapid hydrolysis of the internalized nucleotide sugar. The uptake constituted effective translocation from the medium into the lumen of the vesicles. Thus the amount of vesicle-associated label at equilibrium uptake was directly proportional to the volume of the intravesicular space. Permeabilized microsomes were unable to retain UDPGlcA. The microsomal uptake of UDPGlcA met the criteria of bidirectional carrier-mediated translocation. Transport was time- and temperature-dependent, saturable, selective, capable of trans-stimulation, and operational against a concentration gradient. Microsomal uptake was inhibited by N-ethylmaleimide that was presented at the cytosolic side of the endoplasmic-reticulum (ER) membrane. Uptake studies performed in membrane preparations that were highly enriched in RER, smooth ER or Golgi revealed that UDPGlcA was taken up by the ER as well as by the Golgi apparatus. Our findings demonstrate the existence in rat liver ER of a carrier system mediating proper translocation of intact UDPGlcA across the membrane.

scholarly journals Mechanism of stimulation of microsomal UDP-glucuronosyltransferase by UDP-N-acetylglucosamine

1995 ◽  
Vol 305 (1) ◽  
pp. 321-328 ◽  
Author(s):  
X Bossuyt ◽  
N Blanckaert
Keyword(s):  
Endoplasmic Reticulum ◽  
Glucuronic Acid ◽  
Carrier System ◽  
Transport Pathways ◽  
Weak Inhibitor ◽  
Cytosolic Side ◽  
In Trans ◽  
Udp Glucuronosyltransferase ◽  
Carrier Systems ◽  
Stimulation Of

We propose the existence in rat liver endoplasmic reticulum (ER) of two asymmetric carrier systems. One system couples UDP-N-acetylglucosamine (UDPGlcNAc) transport to UDP-glucuronic acid (UDPGlcA) transport. When UDPGlcNAc was presented at the cytosolic side of the ER, it then acted as a weak inhibitor of UDPGlcA uptake. By contrast, UDPGlcNAc produced a forceful trans-stimulation of microsomal UDPGlcA uptake when it was present within the lumen of the ER. Likewise, cytosolic UDPGlcA strongly trans-stimulated efflux of intravesicular UDPGlcNAc, whereas cytosolic UDPGlcNAc was ineffective in trans-stimulating efflux of UDPGlcA. A second asymmetric carrier system couples UDPGlcNAc transport to UMP transport. Microsomal UDPGlcNAc influx was markedly stimulated by UMP present inside the microsomes. Such stimulation was only apparent when microsomes had been preincubated and thereby preloaded with UMP, indicating that UMP exerted its effect on UDPGlcNAc uptake by trans-stimulation from the lumenal side of the ER membrane. Contrariwise, extravesicular UMP only minimally trans-stimulated efflux of intramicrosomal UDPGlcNAc. It is widely accepted that UDPGlcNAc acts as a physiological activator of hepatic glucuronidation, but the mechanism of this effect has remained elusive. Based on our findings, we propose a model in which the interaction of two asymmetric transport pathways, i.e. UDPGlcA influx coupled to UDPGlcNAc efflux and UDPGlcNAc influx coupled to UMP efflux, combined with intravesicular metabolism of UDPGlcA, forms a mechanism that leads to stimulation of glucuronidation by UDPGlcNAc.

scholarly journals Two kinetically-distinct components of UDP-glucuronic acid transport in rat liver endoplasmic reticulum

1996 ◽  
Vol 1283 (2) ◽  
pp. 223-231 ◽  
Author(s):  
Eric Battaglia ◽  
Susan Nowell ◽  
Richard R. Drake ◽  
Magdalena Mizeracka ◽  
Carl L. Berg ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Rat Liver ◽  
Glucuronic Acid ◽  
Acid Transport

Nuclear membrane-bound UDPglucuronosyltransferase of rat liver

1982 ◽  
Vol 60 (10) ◽  
pp. 972-979 ◽  
Author(s):  
Jan Zaleski ◽  
Surendra K. Bansal ◽  
Teresa Gessner
Keyword(s):  
Endoplasmic Reticulum ◽  
High Activity ◽  
Rat Liver ◽  
Nuclear Membrane ◽  
Glucuronic Acid ◽  
Microsomal Enzyme ◽  
Subcellular Membrane ◽  
Membrane Bound ◽  
Specific Activities

Some properties of rat liver nuclear membrane-bound UDPglucuronosyltransferase were compared with those of the endoplasmic reticulum bound enzyme. The activity of nuclear membrane-bound UDPglucuronosyltransferase was stimulated only about 1.5-fold by Lubrol WX. Under the same conditions microsomal UDPglucuronosyltransferase was, as usual, highly activated (up to 10-fold), when 4-nitrophenol was the acceptor of glucuronic acid. Specific activities of the detergent-activated enzyme were similar in microsomal and nuclear membrane preparations, when the following aglycone substrates were used: 4-methylumbelliferone, 4-nitrophenol, 1-naphthol, phenolphthalein, and testosterone. Apparent Km values for UDP-glucuronic acid ranged between 0.15–0.25 mM for glucuronidation of 4-nitrophenol and 1-naphthol, by either Lubrol WX activated or non-activated, nuclear membrane-bound UDPglucuronosyltransferase. These values were comparable to those found for detergent activated microsomal enzyme. The results show a similarity in behavior of detergent-activated UDPglucuronosyltransferase regardless of subcellular membrane source and, therefore, suggest the association of the same glucuronosyltransferase with nuclear membrane and endoplasmic reticulum. A possible significance of the presence of high activity of this enzyme in nuclear membrane is discussed.

The Role of Membrane Proteins and Phospholipids in the Interaction of Ribosomes with Endoplasmic Reticulum Membranes

1975 ◽  
Vol 53 (9) ◽  
pp. 1039-1045 ◽  
Author(s):  
Serge Jothy ◽  
Jean-Louis Bilodeau ◽  
Henry Simpkins
Keyword(s):  
Endoplasmic Reticulum ◽  
Membrane Proteins ◽  
Rat Liver ◽  
Rough Endoplasmic Reticulum ◽  
Binding Sites ◽  
Molecular Weights ◽  
Low Concentrations ◽  
Phospholipid Headgroups ◽  
Hydrolysis Of

Hydrolysis of the membrane proteins and phospholipid headgroups of rat liver rough endoplasmic reticulum membranes showed that the ribosomal binding sites involve membrane proteins susceptible to low concentrations of trypsin, chymotrypsin, and papain. Three membrane proteins having molecular weights of 120 000, 93 000 and 36 000 are found to be altered by trypsin and chymotrypsin treatment. Also the polar headgroup of phosphatidylinositol appears to play a role in the binding process.

Biosynthesis of Mitochondrial Phospholipids Using Endogenously Generated Diglycerides

1975 ◽  
Vol 53 (7) ◽  
pp. 784-795 ◽  
Author(s):  
W. C. McMurray
Keyword(s):  
Endoplasmic Reticulum ◽  
Phosphatidic Acid ◽  
Phospholipase C ◽  
Rat Liver ◽  
De Novo ◽  
Liver Mitochondria ◽  
Rat Liver Mitochondria ◽  
Isolated Mitochondria ◽  
Hydrolysis Of ◽  
Stimulation Of

When isolated mitochondria or microsomes from rat liver were treated with phospholipase C, the incorporation of radioactive phospholipid precursors was markedly enhanced, presumably as a result of production of diglycerides by hydrolysis of endogenous phospholipids. Incorporation of CDP[14C]choline into lecithin in rat liver or BHK-21 mitochondria could be attributed to residual contamination from elements of the endoplasmic reticulum, with added diglycerides or with endogenous diglycerides produced by the phospholipase C treatment. A similar stimulation of [γ32P]ATP incorporation into phospholipids was observed with exogenous or endogenous diglycerides, but the mitochondrial diglyceride kinase in either case was also related to the degree of microsomal contaminants. It was concluded that previous studies showing negligible capacity of mitochondria for lecithin biosynthesis de novo were not explainable on the basis of limited accessibility of added diglycerides, and that formation of phosphatidic acid by diglyceride kinase was not of significance in rat liver mitochondria.

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