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Query: UMLS:C0027960 (mole)
 21,279 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

1. Mucosal amino acid uptake by pig proximal colon, measured independently for fourteen different amino acids each used at a concentration of 1 mM, ranged from 0.6 to 8.6 n-mole. cm(-2). min(-1) in the new-born to 0 to 0.3 n-mole. cm(-2). min(-1) in the 2-day-old animal. Long chain amino acids entered the mucosa of new-born pig proximal colon much more readily than did short chain amino acids.2. Glycine was used extensively to inhibit the uptake of other neutral amino acids. The degree of maximal inhibition produced depended on the amino acid used. The relative inability of glycine to inhibit the uptake of long chain amino acids suggested that these compounds could cross the brush border on a carrier inaccessible to glycine. The glycine-sensitive uptake remained more or less constant for all amino acids tested (1-2 n-mole.cm(-2).min(-1)); the glycine-insensitive uptake varied from 0 to 7 n-mole.cm(-2).min(-1) (glycine and methionine respectively).3. It is suggested that at least two mechanisms exist for the entry of neutral amino acids into pig proximal colon, one showing specificity for hydrophobic amino acids and the other having broad specificity. The mechanism responsible for the uptake of long chain essential amino acids predominates over the less specific mechanism.4. These results are discussed in relation to previous work carried out on the rabbit ileum where two similar systems for neutral amino acid entry have been shown to be present. Both tissues transport hydrophobic amino acids on their own specific carrier at approximately the same rate; the ability of the pig colon to transport amino acids on the broad specificity carrier is eight times less than in the rabbit ileum. The possibility is raised that this system is subject to regulation.
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PMID:Different mechanisms for neutral amino acid uptake by new-born pig colon. 43 36

Relative partition coefficients of fatty acids and alcohols between aqueous buffers and biological membranes have been determined from the linear relationship between isotope content of sedimented membranes and aqueous concentration. This technique allows study of highly lipid soluble compounds such as long-chain saturated fatty acids. Rat intestinal brush border membranes and erythrocyte ghost membranes were studied by using homologous series of saturated fatty acids, mono-unsaturated fatty acids and 10, 12, and 14 carbon normal alcohols. The influence of chain length on partitioning was similar in the three series with an incremental free energy of -820 cal/mole per methylene group in brush borders for the saturated fatty acids. Incremental enthalpy and entropy were -1331 cal/mole and -1.64 cal/mole, degrees K respectively. Decrease in the partition coefficient due to the double bond (monounsaturated relative to saturated) had an incremental free energy of +1178 cal/mole, incremental enthalpy of -3453 cal/mole, and incremental entropy of -7.34 cal/mole, degrees K, while substitution of the hydroxyl for the ionized carboxyl group (pH 7.4) increased the partition coefficient by 72-fold. From these data it must be concluded that the lipid phase of the membrane bilayer is extremely hydrophobic, similar to heptane or polyethylene in polarity.
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PMID:Fatty acid and alcohol partitioning with intestinal brush border and erythrocyte membranes. 71 16

Suckling rat intestine contains 35 and 65% of the cytosolic and membrane-bound alkaline phosphatase (AP) activities. The corresponding values for sucrase were 20 and 80% respectively. The amount of the soluble enzymes was reduced to 7-11% in adult rat intestine. Administration of cortisone, thyroxine or insulin to suckling animals induced adult type distribution of the enzymes. There were apparent differences in kinetic characteristics of soluble and brush border enzymes, but the kinetic properties of the normally developed and hormone-induced AP and sucrase were essentially similar. This suggested identical nature of these enzymes under these conditions. A biphasic Arrhenius plot was obtained for AP in weaned and hormone injected pups with a break point around 18 degrees C, while the soluble enzyme yielded a monophasic curve (Ea = 8-11 kcal/mole). Arrhenius plot for sucrase was monophasic in the suckling, hormone-injected and adult rat intestine (Ea = 8.3-15.1 kcal/mole). Membrane-bound enzymes were generally labile, while soluble enzyme activities were stable to heat treatment (sucrase at 50 degrees C and AP at 60 degrees C) in various experimental groups.
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PMID:Kinetic characteristics of soluble and brush border alkaline phosphatase and sucrase activities in developing rat intestine: effect of hormones. 235 52

Chicken brush border myosin I (CBB-MI) is a single-headed, nonfilamentous, myosin-like mechanoenzyme which, as isolated, has 3 mol of calmodulin (CAM) 'light chains' bound per mole of 119 kDa heavy chain. We have isolated a partial cDNA clone for CBB-MI that encodes the C-terminal approximately 35 kDa of the heavy chain. The sequence of this clone is identical to that of an authentic, near-full-length CBB-MI cDNA clone reported recently, except for an 87-bp/29-residue insertion occurring approximately 32 kDa from the C-terminus. This insert, which is probably generated by an alternate splicing event, is expressed in brush border as part of a message of the size predicted for the CBB-MI heavy chain, although the steady state level of this transcript is approximately 8-fold lower than for transcripts lacking the insert. 125I-CAM overlays of this cDNA clone (expressed as a trpE fusion protein in E. coli) indicate that it binds one more calmodulin than does a second cDNA clone that lacks the 29-residue insert. A synthetic peptide corresponding to the insert sequence binds tightly to CAM-Sepharose, demonstrates a shift and enhancement of fluorescence in the presence of CAM, and binds CAM in solution with a KD of 190 nM (in 100 mM KCl). We conclude that a second, low-abundance isoform of CBB-MI contains an additional (and possibly fourth) CAM binding site as a result of a 29-residue peptide that is inserted into the tail domain by an apparent alternate splicing event.
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PMID:A second isoform of chicken brush border myosin I contains a 29-residue inserted sequence that binds calmodulin. 236 78

Trehalase (alpha, alpha-trehalase, EC 3.2.1.28) was solubilized from the brush border membrane of pig kidney cortex by Triton X-100 and sodium deoxycholate in the presence of inhibitors of proteolytic enzymes. The kidney enzyme was purified 3060-fold using gel filtration, ion exchange chromatography, Con A-Sepharose chromatography, phenyl-Sepharose CL-4B hydrophobic interaction chromatography, Tris-Sepharose 6B affinity chromatography, and hydroxylapatite chromatography. Tris-Sepharose 6B was utilized to absorb contaminant proteins. Purity was estimated as 99% or greater, based on amino-terminal amino acid analysis. The purified enzyme had a specific activity of 278 units/mg protein, showed one major band after silver staining, and had an estimated molecular weight of 80,000 on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The purified enzyme was a glycoprotein and contained 2 mol of glucosamine per mole of trehalase. Kidney trehalase was inhibited by Tris, HgCl2, and phlorizin with Ki values of 3.8 mM, 11 microM, and 2.4 mM, respectively. Inclusion of Cl- in the reaction mixture protected the enzyme from inactivation by HgCl2. The apparent Km for trehalose was calculated to be 2.1 mM. Kidney trehalase was highly specific for trehalose and exhibited an optimal pH of 5.9. The isoelectric point was between pH 4.7 and 4.4, as measured by chromatofocusing.
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PMID:Purification and properties of detergent-solubilized pig kidney trehalase. 359 57

Water transport mechanisms in rabbit proximal convoluted cell membranes were examined by measurement of: osmotic (Pf) and diffusional (Pd) water permeabilities, inhibition of Pf by mercurials, and activation energies (Ea) for Pf. Pf was measured in PCT brush border (BBMV) and basolateral membrane (BLMV) vesicles, and in viable PCT cells by stopped-flow light scattering; Pd was measured in PCT cells by proton NMR T1 relaxation times using Mn as a paramagnetic quencher. In BLMV, Pf (0.019 cm/sec, 23 degrees C) was inhibited 65% by 5 mM pCMBS and 75% by 300 microM HgCl2 (KI = 42 microM); Ea increased from 3.6 to 7.6 kcal/mole (15-40 degrees C) with 300 microM HgCl2. In BBMV, Pf (0.073 cm/sec, 23 degrees C, Ea = 2.8 kcal/mole, less than 33 degrees C and 13.7 kcal/mole, greater than 33 degrees C) was inhibited 65% with HgCl2 with Ea = 9.4 kcal/mole (15-45 degrees C). Mercurial inhibition in BLMV and BBMV was reversed with 10 microM mercaptoethanol. Viable PCT cells were isolated from renal cortex by Dounce homogenization and differential seiving. Impedence sizing studies show that PCT cells are perfect osmometers (100-1000 mOsm). Assuming a cell surface-to-volume ratio of 25,000 cm-1, Pf was 0.010 +/- 0.002 cm/sec (37 degrees C) and Pd was 0.0032 cm/sec. Pf was independent of osmotic gradient size (25-1000 mOsm) with Ea 2.5 kcal/mole (less than 27 degrees C) and 12.7 kcal/mole (greater than 27 degrees C). Cell Pf was inhibited 53% by 300 microM HgCl2 (23 degrees C) with Ea 6.2 kcal/mole. These findings indicate that cell Pf is not restricted by extracellular or cytoplasmic unstirred layers and that cell Pf is not flow-dependent. The high BLMV and BBMV Pf, inhibition by HgCl2, low Ea which increases with inhibition, and the measured Pf/Pd greater than 1 in cells in the absence of unstirred layers provide strong evidence for the existence of water channels in proximal tubule brush border and basolateral membranes. These channels are similar to those found in erythrocytes and are likely required for rapid PCT transcellular water flow.
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PMID:Evidence for water channels in renal proximal tubule cell membranes. 359 63

The osmotic water permeability Pf of brush border (BBM) and basolateral (BLM) membrane vesicles from rat small intestine and renal cortex was studied by means of stopped-flow spectrophotometry. Scattered light intensity was used to follow vesicular volume changes upon osmotic perturbation with hypertonic mannitol solutions. A theoretical analysis of the relationship of scattered light intensity and vesicular volume justified a simple exponential approximation of the change in scattered light intensity. The rate constants extracted from fits to an exponential function were proportional to the final medium osmolarity as predicted by theory. For intestinal membranes, computer analysis of optical responses fitted well with a single-exponential treatment. For renal membranes a double-exponential treatment was needed, implying two distinct vesicle populations. Pf values for BBM and BLM preparations of small intestine were equal and amount to 60 microns/sec. For renal preparations, Pf values amount to 600 microns/sec for the fast component, BBM as well as BLM, and to 50 (BBM) and 99 (BLM) microns/sec for the slow component. The apparent activation energy for water permeation in intestinal membranes was 13.3 +/- 0.6 and in renal membranes 1.0 +/- 0.3 kCal/mole, between 25 and 35 degrees C. The mercurial sulfhydryl reagent pCMBS inhibited completely and reversibly the high Pf value in renal brush border preparations. These observations suggest that in intestinal membranes water moves through the lipid matrix but that in renal plasma membranes water channels may be involved. From the high Pf values of renal membrane vesicles a transcellular water permeability for proximal tubules can be calculated which amounts to approximately 1 cm/sec. This value allows for an entirely transcellular route for water flow during volume reabsorption.
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PMID:Osmotic water permeabilities of brush border and basolateral membrane vesicles from rat renal cortex and small intestine. 376 62

We have examined the rate-limiting steps involved in bile acid absorption across the unstirred water layer and lipid cell membrane of the jejunal mucosa. Uptake of the polar bile acid taurocholate is limited solely by the cell membrane since this compound permeates the unstirred water layer more rapidly than the lipid cell membrane and stirring does not enhance uptake. With less polar bile acids which permeate the cell membrane relatively more rapidly, however, the unstirred water layer does exert resistance to mucosal uptake of these compounds. That the unstirred water layer is even more rate limiting to uptake from micellar solutions is indicated by the facts that the rate of bile acid absorption from such solutions is lower than from corresponding monomer solutions, stirring markedly enhances uptake from micellar solutions while increases in viscosity of the incubation media depress uptake and expansion of the micelle size further depresses absorption rates. We also have examined the important question of whether the micelle crosses the brush border intact once it reaches the aqueous-lipid interface. The observations that the calculated permeation rate of the micelle should be extremely low, the rate of mucosal cell uptake plateaus at a constant value when the critical micelle concentration is reached at the aqueous-lipid interface, and the different components of a mixed micelle are taken up at different rates indicate that uptake of the intact micelle does not occur; rather, bile acid absorption must be explained in terms of monomers in equilibrium with the micelle. Finally, after correction of the permeability coefficients of the various bile acids for the unstirred layer resistance the incremental partial molar free energy of solution of the hydroxyl group in the brush border membrane was calculated to equal -6126 cal.mole(-1) indicating that passive diffusion of these compounds occurs through a very polar region of the cell membrane.
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PMID:Characterization of bile acid absorption across the unstirred water layer and brush border of the rat jejunum. 467 96

The lipid composition of the brush border membrane (BBM) or apical plasma membrane of enterocytes is characterized by a remarkably high glycosphingolipid content (glycosphingolipid: phospholipid:neutral lipid mole ratio of about 1:1:1). A manifestation of the high glycolipid content of the BBM is the lipid fluidity which is low compared to other mammalian plasma membranes and related to it a steep flexibility gradient: hydrocarbon chain segments close to the lipid-water interface have quasi-crystalline packing while hydrocarbon chain segments close to the centre of the lipid bilayer behave like a fluid. An important function of the BBM is the absorption of dietary lipids. The absorption of cholesterol from bile salt micelles has been shown to be protein-mediated. The integral membrane protein responsible for this activity has features similar to non-specific lipid transfer proteins. Another remarkable property of the BBM is described here: phospholipids are exchanged between the lipid bilayer of the BBM and the lipid bilayers of small unilamellar egg phosphatidylcholine (PC) vesicles. In the course of this probably 1:1 exchange, endogenous BBM phospholipids move out of the BBM and the lipid loss is compensated by the insertion of exogenous PC from the small unilamellar vesicles. This exchange activity is probably due to the same protein(s) responsible for lipid absorption in this membrane or at least related to the absorptive capacity of the BBM. The unique feature of small intestinal BBM is that the on- and off-rate of certain lipids is remarkably high: the underlying structure of this activity is still unknown.
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PMID:A unique feature of lipid dynamics in small intestinal brush border membrane. 776 68

To comprehend the renal defect underlying idiopathic Fanconi syndrome in the Basenji dog, we have focused on delineating the lipid profiles of renal brush border membranes isolated from affected and normal Basenji dogs to establish any physical or compositional changes underlying previously observed transport and membrane-fluidity changes. The lipid composition was studied with respect to total lipid, cholesterol, and phospholipid content, cholesterol to phospholipid ratio, distribution of the major phospholipid classes, and fatty acid composition. Total phospholipid of the isolated renal brush border membranes from Fanconi syndrome dogs analyzed by 31P nuclear magnetic resonance showed no difference compared with that of normal dogs. Examination of total fatty acids in both membranes using gas-liquid chromatography analysis of fatty acid methyl esters showed no difference in the mole percents of the major fatty acids. Our data suggest that changes in bulk membrane fluidity of the Fanconi syndrome dog renal brush border as measured by 1,6-diphenyl-1,3,5-hexatriene cannot be attributed to phospholipid and fatty acid compositional change. In the membranes isolated from affected dog kidney, the cholesterol content determined by gas-liquid chromatography analysis was 66 mol% higher than in membranes isolated from normal dog kidney. This correlates with the higher cholesterol to phospholipid molar ratio of 0.82 +/- 0.08 in the affected animal as compared with 0.58 +/- 0.04 in the normal. Cholesterol content and its microdomain in the membrane bilayer may be important in modulating transport functions. Increased membrane cholesterol content may affect the conformational motility of membrane transport proteins and thus affect their function.
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PMID:Renal brush border membrane lipid composition in Basenji dogs with spontaneous idiopathic Fanconi syndrome. 808 81


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