Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.1.3.1 (alkaline phosphatase)
 47,916 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

An improved analytical procedure for the extraction and determination of total, free and phosphorylated tissue sugar is described. This method, employing ZnSO4 plus Ba(OH)2 for the precipitation of sugar phosphates, yields values identical with those obtained by the more laborious separation of free and phosphorylated sugar by ion-exchange chromatography. Erroneous values for free sugar due to the action of a Zn2+ -activated phosphatase and/or the lability to acids of some sugar phosphates, are avoided. Using this technique for the sudy of transport and phosphorylation of D-galactose in rabbit renal cortical slices and tissue extracts, it was found: 1. The cellular uptake of D-galactose was associated with the appearance of both free and phosphorylated sugar whether or not external Na+ was present. At 1 mM sugar, galactose was accumulated in the cells against a modest concentration gradient of 1.445 +/- 0.097 (n = 17). Galactose phosphate appeared in the cells considerably faster than free sugar under conditions of net uptake as well as of steady-state exchange (pulse-labelling). 2. Increasing saline pH (6-8) increased the cellular levels of sugar phosphate without affecting the steady-state values of free sugar. With tissue extracts, increasing pH also stimulated the activity of galactokinase and the dephosphorylation of galactose 1-phosphate by a Zn2+ -activated phosphatase. 3. 0.5 mM phlorizin inhibited the tissue uptake of galactose and its subsequent oxidation to CO2 only to a minor degree (30 and 10%, respectively). The absence of external Na+ further depressed the phlorizin effect. Preincubation of the tissue with phlorizin and subsequent washing in part abolished the inhibitory effect. The data suggest that a major portion of the galactose uptake by the tissue proceeds by a mechanism with a low affinity for phlorizin. 4. Efflux studies showed that the wash-out of free galactose from slices was associated with a net decrease of both free and phosphorylated tissue sugar. 5. The above results suggest the possibility that phosphorylation may represent a step in the Na+ -independent, phloretin-sensitive transfer of D-galactose across the antiluminal cell membrane. The participation of intracellular galactokinase and a Zn2+ -activated alkaline phosphatase in the maintenance of the steady state of free and phosphorylated galactose in the cells has been demonstrated.
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PMID:Transport and phosphorylation of D-galactose in renal cortical cells. 1 Sep 98

In rats changes in plasma membrane enzyme activities due to Gal-N intoxication were studied by enzymehistochemical methods. The bile canalicular 5'-nucleotidase and nucleoside polyphosphatase activities decreased; the sinusoidal 5'-nucleotidase remained unchanged. The bile canalicular leucyl-beta-naphthyl-amidase showed an increase in activity; the alkaline phosphatase activity remained unchanged. In contrast to the spotty necrosis, changes in plasma membrane enzyme activities were seen in all liver cells, suggesting that changes of these activities, occurring after Gal-N treatment, do not correlate with cell death. The conclusion was drawn that the deviations of the enzyme activities might be due to changes in the lipid environment of the enzyme proteins in the membrane. With the exception of alkaline phosphatase, partial hepatectomy caused the same changes in enzyme activities as did Gal-N intoxication. Nevertheless Gal-N administration to partial hepatectomized rats did not lead to hepatic necrosis. Galactose given simultaneously or within two hours after Gal-N prevented both changes in plasma membrane enzyme activities and hepatocellular damage. This suggests an important role of galactolipids and galactoproteins in the plasma membrane alterations.
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PMID:A histochemical study about changes in rat liver plasma membrane enzyme activities after galactosamine administration. 15 4

A prominent galactose-1-phosphatase was isolated from rat brain and partially purified by chromatography on diethylaminoethyl-Sephacel, hydroxylapatite, and Sephacryl S-300 columns. The galactose-1-phosphatase was separated from alkaline phosphatase, and from two forms of glucose-1-phosphatase. The three columns gave a 10-fold increase in specific activity to 290 mol/min/mg of protein, with a yield of 15%. Of the eight sugar phosphates tested, galactose-1-phosphate was the best substrate for the purified enzyme, followed by glucose-1-phosphate, which was hydrolyzed 40% as rapidly as galactose-1-phosphate. Galactose-1-phosphatase had an optimum pH of 8.5 and a Km value of 2.5 mM for galactose-1-phosphate hydrolysis. Mg2+ was required for activity, and supported half-maximal activity at a concentration of 1.25 mM. Phosphate was the only potent inhibitor found ATP, arsenate, and vanadate caused moderate inhibition of 10 mM levels, whereas AMP, L-homoarginine, and L-phenylalanine stimulated enzyme activity. Galactose-1-phosphatase was determined to have a Stokes radius of 30 A and a sedimentation coefficient of 4.1S. These values were used to calculate a molecular weight of 50,200 and a frictional ratio showing the enzyme to be a globular protein. It is hypothesized that a similar phosphatase may play a role in reducing brain galactose-1-phosphate concentrations in patients with galactosemia.
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PMID:Galactose-1-phosphatase in rat brain. 164 51

Human Caco-2 cells (passage 80 to 100) were seeded onto collagen-coated Millipore filter assemblies and these were maintained in culture either (a) floated on the surface of the medium or (b) submerged within the body of the medium. Structural and functional assessments were made over a 30-day period. After seeding, all cells assumed a flattened, squamous configuration and rapidly became confluent. Cells submerged within the medium formed polarised monolayers with well developed junctional complexes, abundant apical microvilli and increasing levels of alkaline phosphatase activity. Cells grown floated on the surface of the medium formed complex multilayers in which polarisation was confined to the surface layer. Junctional complexes and apical microvilli were similar to those seen in submerged monolayers but alkaline phosphatase activities were higher. Transepithelial electrical resistance increased rapidly from day 1, as the layers became confluent. Electrical resistance was higher and short-circuit current and potential differences were lower across monolayers than across multilayers. After 10 days in culture, the addition of D-glucose to the apical bathing solution, of all cell layers, caused a rapid rise in short-circuit current and potential difference. These changes were sodium-dependent and phlorizin-sensitive. Galactose and 3-O-methylglucose induced similar changes and the affinity constants for these hexoses ranked in the order reported for rat jejunum (Km glucose 2.44 +/- 0.52 mM; Km galactose 8.05 +/- 1.33 mM; Km 3-O-methylglucose 22.0 +/- 5.2 mM). Culture conditions had a marked effect on hexose maximum transport rates (glucose Vmax: submerged 2.94 +/- 0.20 microA/cm2; floated 9.94 +/- 0.82 microA/cm2, P less than 0.05) but affinity constants were unchanged. Apical to basolateral mannitol fluxes, used as an index of paracellular permeability, decreased from day 1 to day 5 and then remained steady. Fluxes across monolayers and multilayers were not significantly different. We conclude that sodium-dependent hexose transport occurs in cultured Caco-2 cell layers grown on permeable supports. Culture conditions, however, have a marked effect on both cell layer structure and function, and should be an important factor when considering Caco-2 cells as an in vitro model of enterocyte function.
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PMID:Active hexose transport across cultured human Caco-2 cells: characterisation and influence of culture conditions. 190 49

The present work investigates the ability of galactose to affect enterocyte differentiation during normal development in vivo. Energy intake has also been varied to take account of the fact that galactose is poorly metabolized in mice. Brush-border lactase, alpha-glucosidase, dipeptidylpeptidase-IV, aminopeptidase N, alkaline phosphatase and microvillus length were measured as markers of enterocyte differentiation in mice fed diets containing galactose (G diet), corn oil (E diet) or galactose + corn oil (G + E diet). Maintaining mice on a G instead of E diet reduced brush-border lactase activity and enterocyte migration rates; alpha-glucosidase, dipeptidylpeptidase-IV, aminopeptidase N and microvillus length expression increased and alkaline phosphatase activity remained unchanged. Feeding the G + E diet restored enterocyte migration rates, lactase, aminopeptidase N and dipeptidylpeptidase-IV activities to values found in mice fed the E diet. Galactose stimulation of alpha-glucosidase and microvillus length expression was, however, fully maintained in mice fed the G + E diet. Present results show that enterocyte differentiation is affected independently by varying dietary galactose and energy levels; that galactose effects always increase and energy effects usually decrease expression of enterocyte components and that energy stimulation of lactase activity is exceptional.
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PMID:Galactose effects on enterocyte differentiation in the mouse jejunum. 190 92

1. Membrane preparations from Klebsiella aerogenes type 8 were shown to transfer glucose and galactose from their uridine diphosphate derivatives to a lipid and to polymer. The ratio of glucose to galactose transfer in both cases was 1:2. This is the same ratio in which these sugars occur in native polysaccharide. Galactose transfer was dependent on prior glucosylation of the lipid. Mutants were obtained lacking (a) glucosyltransferase and (b) galactosyltransferase. The transferase activities in a number of non-mucoid mutants was examined. 2. Glucose transfer was partially inhibited by uridine monophosphate, and incorporation of either glucose or galactose into lipid was decreased in the presence of uridine diphosphate. The sugars are thought to be linked to a lipid through a pyrophosphate bond, and treatment of the lipid intermediates with phenol yielded water-soluble compounds. These could be dephosphorylated with alkaline phosphatase. Transfer of glucuronic acid to lipid or polymer from uridine diphosphate glucuronic acid was much lower than that of the other two sugars. 3. The fate of sugars incorporated into polymer was also followed. Some conversion of glucose into galactose and glucuronic acid occurred. Mutants unable to transfer glucose or galactose to lipid were unable to form polymer. Other mutants capable of lipid glycosylation were in some cases unable to form polymer. A model for capsular polysaccharide synthesis is proposed and its similarity to the formation of other polymers outside the cell membrane is discussed.
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PMID:The synthesis of exopolysaccharide by Klebsiella aerogenes membrane preparations and the involvement of lipid intermediates. 549 69

In Lactococcus lactis subsp. cremoris FD1, galactose and lactose are both transported and phosphorylated by phosphotransferase systems. Lactose 6-phosphate (lactose-6P) is hydrolyzed intracellularly to galactose-6P and glucose. Glucose enters glycolysis as glucose-6P, whereas galactose-6P is metabolized via the tagatose-6P pathway and enters glycolysis at the tagatose diphosphate and fructose diphosphate pool. Galactose would therefore be a gluconeogenic sugar in L. lactis subsp. cremoris FD1, but since fructose 1,6-diphosphatase is not present in this strain, galactose cannot serve as an essential biomass precursor (glucose-6P or fructose-6P) but only as an energy (ATP) source. Analysis of the growth energetics shows that transition from N limitation to limitation by glucose-6P or fructose-6P gives rise to a very high growth-related ATP consumption (152 mmol of ATP per g of biomass) compared with the value in cultures which are not limited by glucose-6P or fructose-6P (15 to 50 mmol of ATP per g of biomass). During lactose metabolism, the galactose flux through the tagatose-6P pathway (r(max) = 1.2 h) is lower than the glucose flux through glycolysis (r(max) = 1.5 h) and intracellular galactose-6P is dephosphorylated; this is followed by expulsion of galactose. Expulsion of a metabolizable sugar has not been reported previously, and the specific rate of galactose expulsion is up to 0.61 g of galactose g of biomass h depending on the lactose flux and the metabolic state of the bacteria. Galactose excreted during batch fermentation on lactose is reabsorbed and metabolized when lactose is depleted from the medium. In vitro incubation of galactose-6P (50 mM) and permeabilized cells (8 g/liter) gives a supernatant containing free galactose (50 mM) but no P(i) (less than 0.5 mM). No organic compound except the liberated galactose is present in sufficient concentration to bind the phosphate. Phosphate is quantitatively recovered in the supernatant as P(i) by hydrolysis with alkaline phosphatase (EC 3.1.3.1), whereas inorganic pyrophosphatase (EC 3.6.1.1) cannot hydrolyze the compound. The results indicate that the unknown phosphate-containing compound might be polyphosphate.
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PMID:Galactose Expulsion during Lactose Metabolism in Lactococcus lactis subsp. cremoris FD1 Due to Dephosphorylation of Intracellular Galactose 6-Phosphate. 1634 33