galactose-6-phosphate and mannose-6-phosphate

Nuclear envelope (NE) and microsomal glucosa-6-phosphatase (G-6-Pase) activities were compared. Intact microsomes were unable to hydrolyze mannose-6-phosphate (M-6-P), on the other hand, intact NE hydrolyzes this substrate. Galactose-6-phosphate showed to be a good substrate for both NE and microsomal enzymes, with similar latency to that obtained with M-6-P using microsomes. In consequence, this substrate was used to measure the NE integrity. The kinetic parameters (Kii and Kis) of the intact NE G-6-Pase for the phlorizin inhibition using glucose-6-phosphate (G-6-P) and M-6-P as substrates, were very similar. The NE T1 transporter was more sensitive to amiloride than the microsomal T1. The microsomal system was more sensitive to N-ethylmalemide (NEM) than the NE and the latter was insensitive to anion transport inhibitors DIDS and SITS, which strongly affect the microsomal enzyme. The above results allowed to postulate the presence of a hexose-6-phosphate transporter in the NE which is able to carry G-6-P and M-6-P, and perhaps other hexose-6-phosphate which could be different from that present in microsomes or, if it is the same, its activity could by modified by the membrane system where it is included. The higher PPi hydrolysis activity of the intact NE G-6-Pase in comparison to the intact microsomal, suggests differences between the Pi/PPi transport (T2) of both systems. The lower sensitivity of the NE G-6-Pase to NEM suggests that the catalytic subunit of this system has some differences with the microsomal isoform.

Topics: 4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid; 4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid; Amiloride; Animals; Antiporters; Diphosphates; Ethylmaleimide; Galactosephosphates; Glucose-6-Phosphatase; Glucose-6-Phosphate; Hydrolysis; Isoenzymes; Liver; Male; Mannosephosphates; Microsomes, Liver; Monosaccharide Transport Proteins; Nuclear Envelope; Phlorhizin; Phosphates; Rats; Rats, Sprague-Dawley; Substrate Specificity

The Escherichia coli uhp T gene encodes an active transport system for sugar phosphates. When the uhp T gene was carried on a multicopy plasmid, amplified levels of transport activity occurred, and growth of these strains was inhibited upon the addition of various sugar phosphates. Two different mechanisms for this growth inhibition were distinguished. Exposure to glucose-6-phosphate, fructose-6-phosphate or mannose-6-phosphate, which enter directly into the glycolytic pathway, resulted in cessation of growth and substantial loss of viability. Cell killing was correlated with the production of the toxic metabolite, methylglyoxal. In contrast, addition of 2-deoxyglucose-6-phosphate, galactose-6-phosphate, glucosamine-6-phosphate or arabinose-5-phosphate, which do not directly enter the glycolytic pathway, resulted in growth inhibition without engendering methylglyoxal production or cell death. Inhibition of growth could result from excessive accumulation of organophosphates in the cell or depletion of inorganic phosphate pools as a result of the sugar-P/Pi exchange process catalysed by UhpT. The phosphate-dependent uptake of glycerol-3-phosphate by the GlpT antiporter was strongly inhibited under conditions of elevated sugar-phosphate transport. There are thus two separate toxic effects of elevated sugar-phosphate transport, one of which was lethal and related to increased flux through glycolysis. It is likely that the control of uhpT transcription by catabolite repression exists to limit the level of UhpT transport activity and thereby prevent the toxic events that result from elevated uptake of its substrates.

Topics: Bacterial Proteins; Biological Transport; Carrier Proteins; Cell Division; Culture Media; Escherichia coli; Escherichia coli Proteins; Fructosephosphates; Galactosephosphates; Gene Expression Regulation, Bacterial; Glucose-6-Phosphate; Glucosephosphates; Glycerophosphates; Glycolysis; Mannosephosphates; Monosaccharide Transport Proteins; Pentosephosphates; Pyruvaldehyde; Sugar Phosphates

In order to study the distribution of endogenous sugar-binding proteins (lectins) in various areas of the adult bovine heart, we used a battery of biotinylated neoglycoproteins. These tools expose carrier-immobilized carbohydrate moieties as ligands for receptor detection. Characteristic staining patterns depending on the type of carbohydrate ligand were observed in all constituents examined. Comparison to data obtained for lectin distribution in the respective areas of the human heart indicate that the localization of certain types of endogenous sugar receptors can exhibit species-dependent variations.

Topics: Animals; Binding Sites; Cattle; Cellobiose; Collagen; Fucose; Galactosephosphates; Histocytochemistry; Lectins; Mannose; Mannosephosphates; Myocardium; Xylose