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

The growth yields of Escherichia coli on glucose, lactose, galactose, maltose, maltotriose, and maltohexaose were estimated under anaerobic conditions in the absence of electron acceptors. The yields on these substrates exhibited significant differences when measured in carbon-limited chemostats at similar growth rates and compared in terms of grams (dry weight) of cells produced per mole of hexose utilized. Maltohexaose was the most efficiently utilized substrate, and galactose was the least efficiently utilized under these conditions. All these sugars were known to be metabolized to glucose 6-phosphate and produced the same pattern of fermentation products. The differences in growth yields were ascribed to differences in energy costs for transport and phosphorylation of these sugars. A formalized treatment of these factors in determining growth yields was established and used to obtain values for the cost of transport and hence the energy-coupling stoichiometries for the transport of substrates via proton symport and binding-protein-dependent mechanisms in vivo. By this approach, the proton-lactose stoichiometry was found to be 1.1 to 1.8 H+ per lactose, equivalent to approximately 0.5 ATP used per lactose transported. The cost of transporting maltose via a binding-protein-dependent mechanism was considerably higher, being over 1 to 1.2 ATP per maltose or maltodextrin transported. The formalized treatment also permitted estimation of the net ATP yield from the metabolism of these sugars; it was calculated that the growth yield data were consistent with the production of 2.8 to 3.2 ATP in the metabolism of glucose 6-phosphate to fermentation products.
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PMID:Influence of transport energization on the growth yield of Escherichia coli. 392 98

We previously reported that concanavalin A could bind specifically to liposomes containing phospholipids and lacking glycoconjugates (Biochem. Biophys. Res. Comm. 74, 208, 1977). In the present study we show that the binding of concanavalin A to the liposomes was greatly increased (up to 5 fold) by the presence of phosphatidylinositol in the liposomes. Furthermore, the binding of concanavalin A to phosphatidylinositol-liposomes was specific and could be inhibited by either alpha-methyl mannoside or by myo-inositol. We also found that concanavalin A-induced lymphocyte mitogenesis could be inhibited either by alpha-methyl mannoside or by myo-inositol. Simultaneous addition of both inhibitors to concanavalin A and liposomes showed that inhibition was non-competitive: alpha-methyl mannoside was more inhibitory to liposomes lacking phosphatidylinositol, and myo-inositol was more inhibitory to liposomes containing phosphatidylinositol. This suggests that the binding site for inositol might be different than that for mannose. Equilibrium dialysis and Scatchard plots revealed 4 binding sites each for inositol and mannose at neutral pH. The binding constants of concanavalin A were 0.13 X 10(4) and 0.25 X 10(4) liters/mole respectively for inositol and mannose. We conclude that concanavalin A binds specifically to the inositol portion of phosphatidylinositol.
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PMID:Specific binding of concanavalin A to free inositol and liposomes containing phosphatidylinositol. 404 Jul 55

Eggs of Urechis caupo are surrounded by a congruent to 0.9 micrometer thick egg envelope and, attached to that, a peripheral jelly layer about 3 micrometers thick. Before fertilization, the sperm undergoes the acrosome reaction and binds to the egg envelope. As part of a study of the induction of the acrosome reaction and sperm binding in Urechis, we have developed a method to prepare an egg envelope fraction by differential centrifugation. The isolation procedure removes much of the jelly layer, but does not alter the fine structure of the envelope. When a sperm contacts an isolated envelope, it undergoes a normal acrosome reaction and binds to the envelope's outer face. Electrophoresis of the envelope fraction on sodium dodecyl sulphate (SDS)/polyacrylamide gels revealed six major components stained by Coomassie Blue, of which four are stained by the periodic acid-Schiff reagents (PAS). To measure the degree of enrichment of the envelope fraction, envelopes were isolated from eggs that had been externally radio-iodinated; the specific activity of the envelope fraction was 17 +/- 3 times greater than that of intact eggs. The amino acid composition of the envelope fraction is dominated by Gly (19 mole %), Asx (11%), Thr (11%), Ser (8%), Ala (8%) and Glx (8%). The sugars fucose, xylose, mannose, galactose, glucose, N-acetylglucosamine and N-acetylgalactosamine were detected by gas-liquid chromatography. We also investigated whether the egg envelope changes at fertilization. No change was detected in the electrophoretic 125I pattern of externally radio-iodinated eggs, and the envelope fractions prepared from unfertilized and fertilized eggs produced the same Coomassie Blue pattern on SDS/polyacrylamide gels.
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PMID:Isolation and partial characterization of Urechis caupo egg envelopes. 404 Sep 20

The serum transferrin from the primate, Macaca fascicularis is isolated by a purification protocol consisting of ammonium sulphate precipitation and column chromatography. The hexose (galactose + mannose) content of Macaca transferrin is 4.7 mole per mole of protein. Quantitative determination of the sialic acid content shows that there are two sialic acid residues per molecule of Macaca transferrin. This conclusion is supported by the neuraminidase treatment of Macaca transferrin, in which there is a 2-step decrease in electrophoretic mobility. Monoferric Macaca transferrins with Fe3+ selectively labelled at the C- and N-terminal sites (TfFec and FeNTf) are prepared at pH 5.5 and 8.5 using ferric dinitrilotriacetate [Fe(NTA)2] chelate and ferrous ammonium sulphate, respectively.
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PMID:Primate (Macaca fascicularis) transferrin: isolation and partial characterization. 405 69

Partially and highly purified sheep LH-releasing factor (LRF) induced secretion of LH during incubations of anterior pituitary slices from ovariectomized ewes treated vaginally or by subcutaneous injection with fluorogestone acetate. The incubation medium contained Krebs-Ringer bicarbonate buffer with glucose, amino acids, mannose, galactose, fucose, glucosamine, galactosamine, sialic acid, calf serum, penicillin, and streptomycin. First, the optimum effect of a dose of 45 mg fluorogestone daily for 12 days before slaughter was demonstrated. These tissues yielded about 2-6 mcg LH per mg tissue in 2 hours. A dose curve of LRF showed 4.7 mcg per mg tissue was optimal, and this dose was adjusted for the purity of the LRF used in subsequent experiments. Added LH, 15.5 mcg highly purified, did not lessen LH production. LH production was fairly constant for 4-5 hours, if the medium were not changed, but increased for up to 7 hours if the medium were renewed. After incubation with labeled amino acids or proline, LH was purified 26-fold over other proteins by ammonium sulfate fractionation DEAE-cellulose chromatography, and Sephadex gel filtration. This LH was biologically active by radioimmunoassay and by the ovary ascorbic acid depletion assay, and of high specific activity, 2.2 Ci per mole LH.
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PMID:[In vitro action of hypothalamic luteinizing hormone releasing factor (IRF) on lamb anterior pituitary. I. Kinetics of excretion of luteinizing hormone (LH)]. 493 8

A thermostable beta-galactosidase (EC 3.2.1.23; beta-dgalactoside galactohydrolase) was found to be inducible in an extreme thermophile resembling Thermus aquaticus. Enzyme induction was achieved by the addition of lactose, galactose, or the alpha-galactoside, melibiose, to growing cultures. The addition of glucose to induced cultures had a repressive effect on further enzyme synthesis. The enzyme was purified 78-fold, and the optimum temperature and pH for activity were determined to be 80 C and pH 5.0, respectively. The enzyme was activated by both manganese and ferrous iron. Sulfhydryl activation and thermal stabilization indicate that the thermophilic beta-galactosidase is a sulfhydryl enzyme. Kinetic determinations at 80 C established a K(m) of 2.0 x 10(-3)m for the chromogenic substrate o-nitrophenyl beta-d-galactopyranoside (ONPG) and a K(1) of 7.5 x 10(-3)m for lactose. The Arrhenius energy of activation (for the hydrolysis of ONPG) was calculated to be 13.7 kcal/mole. A molecular weight of 5.7 x 10(5) daltons was estimated by elution of the enzyme from Sephadex 4B.
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PMID:Induction and characterization of -galactosidase in an extreme thermophile. 502 73

A cellobiose-utilizing bacterium isolated from sugar cane bagasse and identified as a strain of Alcaligenes faecalis (ATCC 21400) produced an inducible beta-glucoside-splitting enzyme. The enzyme was purified by a series of streptomycin and ammonium sulfate fractionations and by Sephadex and diethylaminoethyl column chromatography. The final preparation was purified 130-fold, with a recovery of about 10% of the initial enzyme activity. The enzyme had a wide pH range, with optimal activity at pH 6.0 to 7.0. The enzyme was stable in solution at pH 6.5 to 7.8 when kept at 30 C for 2 hr, but it was destroyed by temperatures above 55 C. At 58 and 60 C, the time required to inactivate 90% of the initial activity was 16 and 6.5 min, respectively. An activation energy of 9,500 cal/mole and a K(m) of 1.25 x 10(-4)m were obtained by using p-nitrophenyl beta-glucoside as a substrate. The K(i) value and hydrolysis of cellobiose by the enzyme indicated a high affinity of the enzyme for the cellobiose. The enzyme had its specificity on beta-glucosidic linkage and the rate of hydrolisis of glucosides depended upon the nature of the aglycon moiety. The inactivation studies showed the presence of sulfhydryl groups in the enzyme. The activity of the enzyme was easily destroyed by the Cu(++) and Hg(++) ions. The Michaelis-Menton relationship and the rate of heat inactivation indicated the presence of one type of noninteracting active site in the bacterial beta-glucosidase. Molecular weight of the enzyme was estimated by gel filtration (Sephadex G-200) and sucrose density gradient, and a value of 120,000 to 160,000 was obtained.
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PMID:Purification and characterization of beta-glucosidase of Alcaligenes faecalis. 536 Dec 17

1. In order to investigate a possible competition for intestinal transport between amino acids and monosaccharides in man, iso-osmotic solutions containing (A) 100 m-mole glycine 1.(-1), (B) 100 m-mole glycine and 200 m-mole monosaccharide (glucose or galactose) 1.(-1), and (C) 200 m-mole monosaccharide 1.(-1), were successively perfused into the upper jejunum of twelve African Zambian patients. None had clinical evidence of malnutrition or small-intestinal disease. By using a double-lumen tube and by reference to a non-absorbable marker (polyethylene glycol, 4000), the rates of absorption of these substances have been calculated for a 30 cm jejunal segment.2. The presence of glucose and galactose produced a significant impairment (up to 50%) in the rate of absorption of glycine. There was also a significant decrease in the uptake of both monosaccharides from the solutions in which glycine was also present.3. If this observation also applies to other amino acids it could have a practical value in population groups living on high carbohydrate diets with a marginal concentration of some essential amino acids. It could have special importance when the jejunal mucosa is damaged in severe malnutrition or gastrointestinal infection. This impairment of amino acid uptake may explain the very high incidence of genetically determined lactase-deficiency in Africa.
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PMID:Impairment of glycine absorption by glucose and galactose in man. 557 47

1. The average rate constant for loss of (45)Ca from an unpoisoned squid axon was 1.8 x 10(-3) min(-1), corresponding to an efflux of 0.2 p-mole/cm(2) sec.2. The Ca efflux from unpoisoned axons was reduced if external calcium was replaced with magnesium, or external sodium with lithium, choline or dextrose. Replacing both sodium and calcium reduced the efflux to about 40%.3. Cyanide caused little immediate change in Ca efflux but after 1(1/2)-2(1/2) hr the efflux increased to 5-15 times its normal value. The effect was rapidly reversed when cyanide was removed.4. The large Ca efflux into cyanide was reduced by a factor of three when external calcium was replaced with magnesium and by a further factor of about six when external sodium was replaced with lithium.5. The Ca efflux from both poisoned and unpoisoned axons had a Q(10) of 2-3, was not affected by ouabain and was greatly reduced by injecting ethyleneglycol bis (aminoethylether)-N,N'-tetra-acetic acid (EGTA).6. After injecting (45)Ca along the axis, the efflux of calcium reached its maximum much more rapidly in a cyanide-treated axon than in an unpoisoned axon.7. Pre-treatment with cyanide greatly increased the rate at which calcium was lost from axoplasm extruded into flattened dialysis bags. A similar effect was observed when cyanide was applied after extrusion.8. Replacing external sodium glutamate with potassium glutamate greatly reduced the loss of (45)Ca from intact axons poisoned with cyanide but had little effect on the loss from extruded axoplasm.9. The rate constant for loss of the Ca EGTA complex was about 3 x 10(-5) min(-1) for intact axons and 2 x 10(-2) min(-1) for extruded axoplasm.10. A possible explanation of the cyanide effect is that, after poisoning, calcium ions are released from a store and can then exchange at a higher rate with external sodium or calcium.11. The experiments suggest that part of the calcium efflux may be coupled to sodium entry.12. Theoretical equations for ;diffusion and chemical reaction in a cylinder' are described in the Appendix.
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PMID:The effect of cyanide on the efflux of calcium from squid axons. 576 8

1. Fifty to ninety per cent of the Na efflux from axons of Loligo forbesi is inhibited by ouabain. The properties of the ouabain-sensitive component of the Na efflux are different from those of the ouabain-insensitive component.2. In unpoisoned axons with an average Na content of 75 m-mole/kg axoplasm the bulk of the ouabain-sensitive Na efflux is dependent on external K.3. In the presence of 460 mM Na in the external medium, raising the external K concentration from 0 to 100 mM increases the ouabain-sensitive Na efflux along a sigmoid curve which shows signs of saturating at high K concentrations.4. The curve relating ouabain-sensitive K influx to external K concentration is similar in shape to that for the ouabain-sensitive Na efflux. At all K concentrations examined the ouabain-sensitive K influx was less than the ouabain-sensitive Na efflux.5. Potassium-free sea water acts rapidly in reducing the Na efflux. There is no appreciable difference between the rates of action of K-free sea water on the Na pump and Na-free sea water on the action potential.6. Caesium and Rb can replace external K in activating the ouabain-sensitive Na efflux. Both the affinity and maximum rate of the Na efflux mechanism are lower when Cs replaces K as the activating cation.7. Isosmotic replacement of external Na by either choline or dextrose, but not Li, increases the affinity of the ouabain-sensitive Na efflux mechanism for external K without appreciably affecting the maximum rate of pumping. External Li behaves like external Na and exerts an inhibitory action on the Na efflux.8. There is a large ouabain-sensitive Na efflux into K-free choline or dextrose sea waters. Addition of either Na or Li to the external medium reduces this efflux along a section of a rectangular hyperbola. The properties of this efflux suggest that there is a residual K concentration of up to 2 mM immediately external to the pumping sites in the axolemma.9. Over the range of internal Na concentrations studied (16-140 m-mole/kg axoplasm) the ouabain-sensitive Na efflux increased linearly with Na concentration.10. Tetrodotoxin (10(-6) g/ml.) reduces the Na influx by about half, but does not affect the ouabain-sensitive Na efflux.11. Isobutanol (1% v/v) reversibly decreases both the ouabain-sensitive and ouabain-insensitive components of the Na efflux.12. Application of 2 mM cyanide to axons immersed in K-free sea water produces a transient rise in the Na efflux. This rise is not seen if ouabain is included in the sea water. The rise in efflux occurs at a time when the axons are partially poisoned and contain adenosine triphosphate (ATP) but no arginine phosphate (ArgP). A similar, but maintained rise can be obtained after application of dinitrophenol (DNP) at pH 8.0. The increased Na efflux in these partially poisoned axons is also inhibited by ouabain.13. Under conditions of partial-poisoning by alkaline DNP, there is a ouabain-sensitive Na influx from K-free sea water. The ouabain-sensitive Na influx is of similar size to the ouabain-sensitive Na efflux. These results show that in partially-poisoned axons immersed in K-free sea water intracellular Na exchanges with extracellular Na in a one-for-one manner by a ouabain-sensitive route. External Li cannot replace external Na in maintaining this process.14. Axons partially poisoned with alkaline DNP are not insensitive to external K. In the absence of external Na their response to external K is essentially the same as that seen in unpoisoned axons.15. Possible mechanisms are discussed for the appearance of Na-Na exchange in partially poisoned axons.
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PMID:The ouabain-sensitive fluxes of sodium and potassium in squid giant axons. 581 24


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