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C Wraight

Publications and source records attributed to C Wraight.

7 recordsLinked to original sources
PubMed1993

TGN38 is maintained in the trans-Golgi network by a tyrosine-containing motif in the cytoplasmic domain.

Sorting of proteins destined for different plasma membrane domains, lysosomes and secretory pathways takes place in the trans-Golgi network (TGN). TGN38 is an integral membrane protein found in this intracellular compartment. We show that TGN38 contains an autonomous targeting signal within its cytoplasmic domain which determines its intracellular location. Deletion analysis and site-directed mutagenesis of this domain demonstrate that a tyrosine motif homologous to the internalization signal of surface receptors is necessary and sufficient for correct localization. These findings suggest that TGN38 is maintained in the TGN by retrieval from the plasma membrane and employs a different mechanism for retention from that of the transferase enzymes of the trans-Golgi.

Amino Acid Sequence↗
PubMed1989

MHC class II invariant chains in antigen processing and presentation.

Most protein antigens cannot elicit a T-cell response unless they are processed to peptides, which are then presented to T lymphocytes by surface MHC class II molecules. Recent evidence supports an essential role of the invariant chain associated with class II MHC polypeptides in antigen processing.

Antigens↗
PubMed1988

Dietary regulation of ornithine transcarbamylase mRNA in liver and small intestine.

In the rat, changes in dietary protein intake give rise to changes in the levels of ornithine transcarbamylase (OTC) in liver and small intestine--an increase in liver and decrease in small intestine. The changes in enzyme level are accompanied by similar changes in levels of specific mRNA. Thus in liver, there is an increase in the level of specific mRNA when protein intake is increased, whereas in small intestine there is a small decrease. Comparison of changes in specific mRNA with total poly-A-containing RNA showed that the change in OTC mRNA in liver paralleled the change in total RNA levels. In contrast, in small intestine the small decrease in OTC mRNA levels when protein intake was increased was in the face of an increase in the level of total mRNA. Whereas the level of OTC is 20-fold higher in liver than in small intestine, the mRNA level for the enzyme differs by only 2.5-fold.

Animals↗
PubMed1985

Comparison of ornithine transcarbamylase from rat liver and intestine. Evidence for differential regulation of enzyme levels.

Ornithine transcarbamylase (OTCase) was purified from the small intestine of rat and the properties of the gut enzyme were compared with those of the enzyme from liver. The enzymes from both sources bound to the transition-state analog inhibitor, delta-N-(phosphonoacetyl)-L-ornithine, immobilized on Sepharose and eluted with carbamyl phosphate as a homogeneous preparation. The specific activities of the pure enzymes were 966 mumol min-1 mg-1 and 928 mumol min-1 mg-1 from liver and gut respectively, and the molecular mass, based on electrophoretic mobility, was 38 000 Da. The isoelectric point of the enzymes from both sources was 7.3. The enzymes from both sources cross-react to the same extent with antibodies against the liver enzyme on Western transfers and the size of the mRNA was identical on Northern transfers probed with a cDNA for the liver enzyme. Although OTCase is apparently the same gene product in both liver and gut, the enzyme levels respond differently to alterations in the protein content of the diet. OTCase in liver increased from 0.76 mumol min-1 microgram-1 DNA on 15% casein to 1.3 mumol min-1 microgram-1 DNA on 60% casein (P less than 0.01) whereas in small intestine the level decreased from 8.8 nmol min-1 microgram DNA on 15% casein to 5.7 nmol min-1 microgram-1 DNA on 60% casein (P less than 0.05). When expressed on a fresh-weight basis, the enzyme activity in liver shows the characteristic increase with increasing protein, whereas the activity in gut does not. The connection between these differences in gene expression and the different physiological roles of OTCase in liver and gut is discussed.

Animals↗
PubMed1985

A two-step purification of ATP-citrate lyase from rat liver and its use in a fluorometric assay for N-acetylglutamate synthetase.

ATP-citrate lyase (EC 4.1.3.8) was purified to homogeneity from the liver of rats maintained on a diet containing no fat and high carbohydrate. The procedure involves two steps: dye-ligand chromatography on yellow MX-6G Sepharose CL-4B and ion-exchange chromatography on DEAE-Trisacryl. The specific activity of the enzyme was 10 mumol X min-1 X mg-1 at 25 degrees C, which is equal to the highest specific activity reported to date. The yield was also the highest reported to date, being in excess of 50%, and the enzyme isolated by this procedure has little proteolytic nicking. The pure enzyme was used to establish a coupled fluorometric assay for N-acetylglutamate synthetase (amino-acid acetyltransferase, EC 2.3.1.1) based on coupling coenzyme A production to the oxidation of NADH via ATP-citrate lyase and malate dehydrogenase. The method is easy to perform compared with existing methods and enables the measurement of 100 pmol X min-1 of N-acetylglutamate synthetase activity. The method is generally applicable for measurement of enzymes which produce coenzyme A. The fluorometric method was used to measure the Km for glutamate and acetyl coenzyme A at pH 7.0 and 25 degrees C, which were 8.2 and 0.4 mM, respectively. Arginine at 1 microM gave half-maximal activation of N-acetylglutamate synthetase.

ATP Citrate (pro-S)-Lyase↗
PubMed1985

Inhibition of intestinal citrulline synthesis causes severe growth retardation in rats.

delta-N-(phosphonacetyl)-L-ornithine (PALO) is a powerful and specific inhibitor of ornithine transcarbamylase (1), but it does not readily enter intact cells and therefore does not inhibit citrulline synthesis in intact liver or intestine. We have used the glycylglycine derivative of PALO (Gly-Gly-PALO) to evaluate the importance of intestinal citrulline synthesis in supplying arginine for growth. We have shown that the peptide derivative of PALO is selectively taken up by gut cells via the peptide permease and is released intracellularly as the free inhibitor. When administered in drinking water to 6-wk-old rat pups on an arginine-deficient diet, serum citrulline was reduced from 85 +/- 4.2 to 44 +/- 2.2 microM and arginine from 240.1 +/- 19.0 to 52.1 +/- 4.1 microM. Ornithine increased from 100 +/- 6.2 to 273.5 +/- 21.3 microM. Addition of 0.1 mM Gly-Gly-PALO to drinking water caused a rapid and complete inhibition of growth in rats on arginine-deficient diets, and this growth inhibition could be partially prevented by simultaneous administration of 1% (wt/wt) arginine to the diet and completely prevented with 1% (wt/wt) citrulline. The specificity of the effects of Gly-Gly-PALO on intestinal citrulline synthesis was shown by the inability of the drug to be taken up or to inhibit citrulline synthesis in isolated rat hepatocytes, and the oral administration of the drug had no effect on serum ammonia concentrations. The relative importance of endogenous synthesis of arginine compared with dietary arginine for growth was shown by the ability of Gly-Gly-PALO to inhibit the growth of rats maintained on standard laboratory chow containing normal levels of arginine.

Animals↗