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

Samples of lobster hemocyanin (Homarus americanus) under conditions of reversible reaction between whole (25 S) and half (17 S) molecules have been subjected to accurately known nitrogen pressures in analytical ultracentrifuge cells. A modified pressurization chamber of the type developed by Schumaker and colleagues has been constructed for this purpose. The molecular weight was then determined at the top (liquid-gas) meniscus, by means of the Archibald method. The logarithmic dependence upon pressure of the derived equilibrium constant then gave directly the volume of reaction. Experiments were performed in veronal-citrate buffers at pH 8, where the molar volume of formation of whole (dodecameric) molecules from half molecules appears to be negative, and at pH 8.46 in veronal-citrate buffer in the presence of 0.003 molar free calcium ion, where the molar volume of formation was estimated to be + 390 cm3/mole. In glycine-sodium hydroxide buffer at pH 9.6 containing 0.0047 molar free calcium, the molar volume of formation of whole molecules was estimated to be +120 +/- 70 cm3, corresponding to an estimated difference in partial specific volume between whole molecules and half molecules of only 1.3 (10)-4cm3/gram. The correctness of the sign of this value in glycine buffer has been verified by pressure-jump light-scattering experiments.
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PMID:Volume of reaction by the Archibald ultracentrifuge method (lobster hemocyanin). 96 12

A subepidermal calcified nodule occurred on the face of a 15-year-old Negro boy. Histological examination revealed its apparent origin in mature and immature hair follicles. Previous reports suggest that subepidermal calcified nodules may arise in nevi or in sweat glands. An additional finding in this case was transepidermal elimination of calcium.
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PMID:Subepidermal calcified nodule. Report of a case with apparent hair follicle origin. 99 97

The actomyosin complex of human myometrium has a low Ca-activated ATPase activity (0.007-0.012 mu mole H+ per 1 mg protein for 1 min), small degree and rate of superprecipitation. Transition to the state of pregnancy is accompanied by considerable changes in the physicochemical properties of the myometrium actomyosin. ATPase activity is 5-10 times as high and the rate of superprecipitation rises, particularly after the increase in the calcium concentration. The content of nucleic acid in the actomyosin complex decreases and D280/D260=1.1. The intensity of the actomyosin fluorescence at the pregnant state is more than twice as high.
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PMID:[Physico-chemical properties of uterine smooth muscle actomyosin]. 101 39

Kinetic results of the crystal growth and dissolution of seed crystals of calcium fluoride and magnesium fluoride, obtained conductimetrically and potentiometrically, indicate that both processes are controlled by a surface reaction mechanism. An initial reaction surge in the case of magnesium fluoride is consistent with a concomitant secondary nucleation process. The activation energies for the growth and dissolution of calcium fluoride, 14.5 and 1.4 kcal mole-1, also point to surface reaction control. The heat of solution of this salt, obtained calorimetrically, was 2.9 +/- 0.1 kcal mole-1.
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PMID:Kinetics of crystal growth and dissolution of calcium and magnesium fluorides. 106 44

A review of the surface chemistry of bone mineral, hydroxyapatite and amorphous calcium phosphate is presented. Small-angle x-ray scattering and low-temperature nitrogen adsorption measurements show the magnitude of bone mineral surface to range from 100-200 m-2/g; the synthetic hydroxyapatite surface can vary from 25-200 m-2/g, while synthetic amorphous calcium phosphate ranges in surface from 20-60 m-2/g, according to the respective preparation conditions. The magnitude of heats of adsorption of certain small molecules (CO, Ar, N2, H2O, CH3OH) on bone mineral and hydroxyapatite show that these are polarizing surfaces that form strong bonds with polar or polarizable molecules; water is hydrogen-bonded to these surfaces with energies ranging from 23 kcal/mole for low coverage to 11 kcal/mole after two full monolayers; concomitantly, methanol ranges from 24 kcal/mole to 9 kcal/mole after the adsorption of one and a half monolayers. Stearic acid will close-pack perpendicularly on bone apatite surfaces when adsorbed from cyclohexane solution in a way reminiscent of the adsorption of this long, straight-chain molecule on water surface. It is believed that these molecules are hydrogen-bonded to electronegative ions on the apatite surface. Synthetic hydroxyapatite has long been used in chromatographic adsorption columns because of the specific bonding capacity the surfaces have for certain proteins and polynucleotides. The metabolic interrelationship of bone mineral and the body fluids is in great part dependent upon the nature and magnitude of mineral surface. From the surface studies described herein it was suggested that a chemical linkage could exist in bone between the mineral surface and certain free polar groups of collagen.
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PMID:The surface chemistry of bone mineral and related calcium phosphates. 109 77

1. The orgin of the calcium secreted by the pancreas has been investigated in vivo in the guinea-pig by a study carried out in parallel (a) in the juice secreted in response to the injection of either secretin or caerulein and (b) in the pancreatic tissue and in cell fractions isolated thereform. 2. In agreement with previous findings we observed that the concentration of calcium is low in the secretin-stimulated and high in the caerulein-stimulated juice. In the latter calcium and protein are proportional (cal0 n-mole:mg). 3. After I.V. injection of 45Ca the radioactivity decreases rapidly and quasi-exponentially in the blood plasma. A roughly parallel time course is found in the secretin-stimulated juice: the evolution of the juice: plasma radioactivity ratio resembles that observed with the extraceullar space marker [3H]D-sorbitol. In contrast, the time course of 45Ca in plasma and caerulein-stimulated juice are not proportional: the high levels characteristic of this juice are reached several minutes after the injection and maintained thereafter. This increase is followed ca. 50 min later by the appearance of the newly synthesized [3H]L-leucine-labelled proteins. 4. The pancreatic tissue is rich in calcium which is localized primarily in zymogen granules (Ca.36 n-mole:mg protein) and mitochondria; the soluble cytoplasm is low in calcium. 5. The injected 45Ca accumulates in zymogen granules faster than [3H]L-leucine-labelled proteins. The 45Ca:protein ratio of these organelles is considerably lower than that of the caerulein-stimulated juice. 6. It is concluded (a) that calcium is secreted in to the pancreatic juice in two fractions, one (possibly released by simple diffusion) associated with the electrolyte component, the other with protein of the juice, (b) that zymogen granules are the major, but not the only source of the latter fraction, and (c) that the zymogen granule-associated calcium joins the exportable proteins some time after their synthesis, possibly in the Golgi complex and/or in the condensing vacuoles.
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PMID:Secretion of calcium in pancreatic juice. 114 21

A study of the equilibrium binding of ADP, 1,N6-ethenoadenosine diphosphate, adenylyl imidodiphosphate, and 1,N6-ethenoadenylyl imidodiphosphate to solubilized spinach chloroplast coupling factor 1 (CF1) has been carried out. All four nucleotides were found to bind to two apparently identical "tight" sites, with characteristic dissociation contants generally less than 10 muM. The binding to these "tight" sites is similar in the presence of Mg2+ and Ca2+, is stronger in 0.1 M NaC1 than in 20 mM Tris-C1, and is only slightly altered by heat activation. The slow rate of association of ADP and 1,N6-ethenoadenosine diphosphate at these sites rules out the possibility that they are catalytic sites for ATPase activity on the solubilized enzyme. A third tight site for adenylyl imidodiphosphate was found on the heat-activated enzyme. The dissociation constant for this interaction (7.6 muM) is similar to the adenylyl imidodiphosphate competitive inhibition constant for ATPase activity (4 muM). ADP, which inhibits ATPase activity but is not a strong competitive inhibitor, binds only weakly at a third site (dissociation constant greater than 70 muM). One mole of 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole reacted per mole of CF1 prevents ADP and adenylyl imidodiphosphate binding at the "catalytic" site and abolishes the ATPase activity. A model is proposed in which the "tight" nucleotide binding sites act as allosteric conformational switches for the ATPase activity of solubilizedCF1.
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PMID:Characterization of nucleotide binding sites on chloroplast coupling factor 1. 114 87

Cation permeability and lipid composition have been studied in the red cells of five patients with various features of the hereditary stomatocytosis syndrome. Hemolysis was compensated in four patients, and only one patient was anemic. Cell NA+ was increased an average of 3 mueq per ml cells and cell K+ decreased 14 mueq per ml cells. Both active and passive fluxes of Na+ and K+ were increased by two to six times normal. Tritiated ouabain binding was increased an average of 2.5-fold, suggesting a proportionally greater number of cation pumps per cell. The coupling ratio of active Na+:K+ fluxes was normal (3:2). Calcium permeability was increased compatible with the degree of reticulocytosis, and cell Ca2+ content was normal. The lowered sum of Na+ plus K+ was associated with a high MCHC and low cell water. When examined in wet preparations, red cells assumed either a bowl-shaped or an irregular contour, and they appeared as target cells on dry smears. Only when cell water was increased in hypotonic media were stomatocytes seen on smear. The total lipid content of red cells was increased in four patients, although it was normal in one. The mole ratio of cholesterol to phospholipid was always normal; however, phospholipid analysis showed an increased proportion of phosphatidyl choline. The abnormal cells were osmotically resistant due to both an increased membrane surface area and a low total cation content. These patients show two hallmarks of hereditary stomatocytosis: bowlshaped red cells observed on wet preparations and a marked increase in Na+ and K+ permeability. The heterogeneity of this syndrome in our patients and in others reported with hereditary stomatocytosis appears to result from (1) variability in the increase in surface area which results from an excess of membrane lipid content, particularly phosphatidylcholine, and (2) a variability in cell water content which may be either decreased or increased as a result of changes in the sum of Na+ plus K+ ions.
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PMID:Characteristics of the membrane defect in the hereditary stomatocytosis syndrome. 114 92

1. Membrane potentials have been recorded from cells of seminiferous tubules of rats in vitro using micro-electrodes. The value in 808 impalements was -28-2 +/- 0-3 mV (mean +/- S.E.) at 33 degrees C. 2. Increasing the potassium concentration depolarized the cells, a tenfold increase in concentration causing a depolarization of 16 mV. Removal of sodium from the bathing solution caused a hyperpolarization of 3 mV at a potassium concentration of 5-9 m-equiv/l. Removal of chloride and replacement with impermeant anions had no effect on potential. Removal of calcium from the bathing solution caused a minor but significant depolarization. 3. Ouabain (10-3 M), dinitrophenol (2-5 times 10-4 M) or removal of glucose from the bathing fluid all caused depolarization. The membrane potentials of the cells were sensitive to temperature over the range 10-33 degrees C, the apparent activation energy for the reactions maintaining the potential being approximately 6 kcal/mole. 4. Membrane potentials in seminiferous tubules were independent of age of the animal, were insensitive to previous hypophysectomy and were insensitive to a number of hormones (FSH, LH, HCG, oxytocin). In high concentration prostaglandin E1 caused depolarization. 5. Acetazoleamide (4 times 10-5 M) caused a rapid, but reversible, depolarization of the tubular cells. This was also true in conditions when the HCO'3/CO2 buffer system was replaced with Tris-buffer. Another carbonic anhydrase inhibitor (p-sulphonamido-benzoic acid) had similar effects on cell potentials as acetazoleamide. These results are discussed in relation to the nature of the ionic secretion produced in the tubules. 6. Occasional cells showed phasic variations in membrane potential. A possible connexion between these variations and the contractile activity of the tubules is discussed.
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PMID:Intracellular potentials in cells of the seminiferous tubules of rats. 115 7

To evaluate better the physicochemical characteristics of human fat digestion, a method was developed which allowed characterization of the bile acid-lipid mixed micelles of the aqueous phase of post-prandial duodenal fluid. Duodenal fluid was collected after a 36-g fat breakfast for two 90-min periods and for 60 min after i.v. cholecystokinin and was ultracentrifuged at 15,400,000 g-min. The aqueous phase was isolated, passed through a 200-nm filter, and the mixed micelles were concentrated by an ultrafiltration procedure using a 1.5-nm filter. The 1.5-nm retentate was eluted from Sepharose 6B columns with 1.5-nm filtrate for both preequilibration fluid and eluent. 1.5-nm filtrate approximated the monomer concentrations. Each sample was assayed for bile acid, fatty acid, lecithin, lysolecithin, protein, cholesterol, and counterions (pH, Na+, K+, Ca2+). Constituents were concentrated only on the 1.5-nm filter. On gel permeation chromatography, coincident peaks were observed for bile acid, fatty acid, lysolecithin, and cholesterol; and were eluted with a Kav range of 0.50-0.68 (corresponding to a Stokes radius of 2.3-3.5 nm). An average density of 1.25 and coincident peaks of bile acid and fatty acid were found for the mixed micelles on sucrose density gradients. The regression lines of micellar fatty acid, lysolecithin, and cholesterol vs. bile acid gave a stoichiometry of 1.4 mol fatty acid, 0.15 mol lysolecithin, and 0.06 mol cholesterol for each mole of bile acid. Mixed micelles were homogeneous in composition. These results provide direct evidence for the existence of the postprandial mixed micelle and describe several of its physicochemical properties.
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PMID:Isolation and properties of the mixed lipid micelles present in intestinal content during fat digestion in man. 115 87


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