Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.1.3.9 (glucose-6-phosphatase)
 3,081 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Glycoprotein processing in Dictyostelium discoideum is characterized by enzyme catalyzed steps not reported in other organisms. One of these is the formation of a beta 1 --> 4 linkage between GlcNAc and the mannose linked to the core mannose in the alpha 1 --> 6 position of N-glycosides. A simple and sensitive assay for this GlcNAc transferase activity, using a tri-mannose acceptor and a low concentration of UDP-GlcNAc, was developed. Homogenates of the organism were subjected to sub-cellular fractionation by centrifugation in discontinuous sucrose gradients. The specific activity was enriched 4-5-fold in a crude membrane fraction. The transferase was purified 10-12-fold in a membrane fraction that bands on top of 1.1 M sucrose. This fraction was also enriched in nucleotidyldiphosphatase. The enriched fraction was deficient in glucose-6-phosphatase, an endoplasmic reticulum marker. Approx. 80% of the transferase activity was latent, and unavailable to protease. Purified membranes were either subjected to phase separation in Triton X-114, or sodium carbonate extraction or sonication. In each case, the transferase behaved as an intrinsic membrane protein. Several secreted and lysosomal proteins are modified by the enzyme. These data support the idea that the GlcNAc transferase is present as an integral Golgi membrane protein and that at least the catalytic center of the transferase is on the lumenal side of the vesicles.
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PMID:Subcellular distribution of "intersecting' beta-N-acetylglucosaminyltransferase in Dictyostelium discoideum. A likely marker for the Golgi apparatus. 865 99

The development of Dictyostelium discoideum is a model for tissue size regulation, as these cells form groups of approximately 2 x 10(4) cells. The group size is regulated in part by a negative feedback pathway mediated by a secreted multipolypeptide complex called counting factor (CF). CF signal transduction involves decreasing intracellular CF glucose levels. A component of CF, countin, has the bioactivity of the entire CF complex, and an 8-min exposure of cells to recombinant countin decreases intracellular glucose levels. To understand how CF regulates intracellular glucose, we examined the effect of CF on enzymes involved in glucose metabolism. Exposure of cells to CF has little effect on amylase or glycogen phosphorylase, enzymes involved in glucose production from glycogen. Glucokinase activity (the first specific step of glycolysis) is inhibited by high levels of CF but is not affected by an 8-min exposure to countin. The second enzyme specific for glycolysis, phosphofructokinase, is not regulated by CF. There are two corresponding enzymes in the gluconeogenesis pathway, fructose-1,6-bisphosphatase and glucose-6-phosphatase. The first is not regulated by CF or countin, whereas glucose-6-phosphatase is regulated by both CF and an 8-min exposure to countin. The countin-induced changes in the Km and Vmax of glucose-6-phosphatase cause a decrease in glucose production that can account for the countin-induced decrease in intracellular glucose levels. It thus appears that part of the CF signal transduction pathway involves inhibiting the activity of glucose-6-phosphatase, decreasing intracellular glucose levels and affecting the levels of other metabolites, to regulate group size.
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PMID:Exposure of cells to a cell number-counting factor decreases the activity of glucose-6-phosphatase to decrease intracellular glucose levels in Dictyostelium discoideum. 1564 62

A method for the isolation and purification of plasma membranes of Dictyostelium discoideum by equilibrium centrifugation on sucrose followed by Renografin continuous density gradients has been developed and monitored both with electron microscopy and a number of enzyme assays. On electron microscopy, the final plasma membrane fractions are judged to be freethe basis of of nuclei, rough endoplasmic reticulum, lysosomes and peroxisomes. Some profiles of the mitochondrial inner membranes are found within the plasma membrane fractions, but this contamination has been estimated to be only 5%. On the basis on enzyme assays, the plasma membrane fractions contain all the 5'-nucleotidase activity in the final gradients and are free of catalase, acid phosphatase and malate dehydrogenase activity (markers for peroxisomes, lysosomes, soluble enzymes and the matrix of mitochondria). Their content of glucose-6-phosphatase is reduced by more than 70%. The large majority of RNA and DNA have been removed from the preparation.
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PMID:The involvement of the plasma membrane in the development of Dictyostelium discoideum. I. Purification of the plasma membrane. 1625 Mar 37

Dictyostelium discoideum form groups of approximately 2 x 10(4) cells. The group size is regulated in part by a negative feedback pathway mediated by a secreted multipolypeptide complex called counting factor (CF). The CF signal transduction pathway involves CF-repressing internal glucose levels by increasing the K(m) of glucose-6-phosphatase. Little is known about how this enzyme is regulated. Glucose-6-phosphatase is associated with microsomes in both Dictyostelium and mammals. We find that the activity of glucose-6-phosphatase in crude microsomes from cells with high, normal, or low CF activity had a negative correlation with the amount of CF present in these cell lines. In crude cytosols (supernatants from ultracentrifugation of cell lysates), the glucose-6-phosphatase activity had a positive correlation with CF accumulation. The crude cytosols were further fractionated into a fraction containing molecules greater than 10 kDa (S>10K) and molecules less than 10 KDa (S<10K). S>10K from wild-type cells strongly repressed the activity of glucose-6-phosphatase in wild-type microsomes, whereas S>10K from countin(-) cells (cells with low CF activity) significantly increased the activity of glucose-6-phosphatase in wild-type microsomes by decreasing K(m). The regulatory activities in the wild-type and countin(-) S>10Ks are heat-labile and protease-sensitive, suggesting that they are proteins. S<10K from both wild-type and countin(-) cells did not significantly change glucose-6-phosphatase activity. Together, the data suggest that, as a part of a pathway modulating multicellular group size, CF regulates one or more proteins greater than 10 KDa in crude cytosol that affect microsome-associated glucose-6-phosphatase activity.
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PMID:A protein in crude cytosol regulates glucose-6-phosphatase activity in crude microsomes to regulate group size in Dictyostelium. 1660 21

It is still not clear how organisms regulate the size of appendages or organs during development. During development, Dictyostelium discoideum cells form groups of approximately 2 x 10(4) cells. The cells secrete a protein complex called counting factor (CF) that allows them to sense the local cell density. If there are too many cells in a group, as indicated by high extracellular concentrations of CF, the cells break up the group by decreasing cell-cell adhesion and increasing random cell motility. As a part of the signal transduction pathway, CF decreases the activity of glucose-6-phosphatase to decrease internal glucose levels. CF also decreases the levels of fructose-1,6-bisphosphate and increases the levels of glucose-6-phosphate and fructose-6-phosphate. In this report, we focus on how a secreted signal used to regulate the size of a group of cells regulates many basic aspects of cell metabolism, including the levels of pyruvate, lactate, and ATP, and oxygen consumption.
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PMID:A cell number counting factor alters cell metabolism. 1972 69