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

1. The effect of acute alterations of plasma sodium concentration (PNa) on renal sodium excretion (UNaV) was investigated by three types of experiments on anaesthetized dogs: (a) A local increase in PNa at one kidney was produced by infusion of hypertonic saline directly into its artery while systemic levels of PNa were stabilized by haemodialysis. (b) Systemic levels of PNa were lowered by exchange transfusion of blood for an equal volume of salt-free dextran-in-dextrose solution. The results were contrasted with those observed after similar exchanges, but using dextran-in-saline solution. (c) The level of PNa was altered by varying the sodium concentration of a saline solution infused at a fixed rate either intravenously or into one renal artery. 2. All three types of experiment suggest a dependence of UNaV on PNa Analysis demonstrated that this relationship was not due to contemporary changes in: packed cell volume; plasma solids concentration; plasma potassium concentration; blood pressure or plasma hydrogen ion concentration. The distribution of these variables did not change with PNa except for plasma hydrogen ion concentration. Moreover, the relationship persisted when data were selected to exclude clearance periods in which the value for any variable had shifted past the group mean obtained before PNa was altered. 3. The fall in UNaV at low levels of PNa could be attributed to a fall in glomerular filtration rate (GFR), but the progressive rise in UNaV seen as PNa exceeded 150 m-mole 1(-1) occurred despite a fall in GFR and no apparent change in the mean filtered load of sodium. These results suggest that the increased sodium excretion accompanying raised levels of PNa is due to reduced tubular re-absorption of sodium.
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PMID:Plasma sodium concentration and sodium excretion in the anaesthetized dog. 0 71

D-Erythrulose reductase of beef liver was crystallized from ammonium sulfate solution at pH 8.17. The crystals are needle-shaped. The enzyme protein contains 851 amino acid residues per mole of the enzyme: Lys28, His11, Arg52, Asp79, Thr58, Ser56, Glu68, Pro20, Gly80, Ala107, Val112, Met24, Ile31, Leu88, Tyr7, Phe22, Trp4, and Cys4. The enzyme is inactivated by exposure to temperatures below 12degrees. The inactivation is accelerated by increasing the salt concentration and decreasing the enzyme concentration. The pH of the medium also has a pronounced effect, the maximum stability of the enzyme is obtained at pH 8.5. NADP+ protected the enzyme from cold inactivation at all stages of the process and also afforded protection against inactivation by heat and pH. The cold inactivation of the enzyme is accompanied by dissociation of the enzyme protein to subunits.
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PMID:Studies on D-tetrose metabolism. VI. Crystallization and some properties of D-erythrulose reducatase from beef liver. 0 10

The oxygen-binding characteristics and the multiplicity of the stripped hemoglobiin from active lungfish Protopterus amphibius, are the same as in specimens that have been estivating for about 30 months, showing that alteration in the hemoglobin molecules is not involved in the earlier reported increase in oxygen affinity of whole blood during estivation (Johansen et al., '76). At pH 7.0 and 26 degrees C the hemolysates show a high oxygen affinity (P50 = 3.1 Torr), a Bohr factor (delta log P50/delta pH) of - 0.33, and a cooperativity coefficient (n) of 1.7. Between 15 and 26 degrees C, the apparent heat of oxygenation (delta H) is - 8.6 Kcal-mole-1 at pH 7.0, corresponding with data for other fish. A low sensitivity of oxygen affinity to urea appears to be adaptive to the high urea concentrations in estivating lungfish. The salt sensitivity is, however, similar to human hemoglobin. The hemoglobin consists of two major (electrophoretically anodal) components, which differ slightly in oxygen affinity but are both sensitive to pH and nucleoside triphosphates (NTP). Guanosine triphosphate (GTP), the major erythrocytic organic phosphate, however, depresses the oxygen affinity of the composite and separated hemoglobins more effectively than ATP suggesting that GTP is the primary modulator of oxygen affinity. Comparative measurements reveal only one major hemoglobin component in P. annectens which has a markedly lower oxygen affinity and phosphate sensitivity than P. amphibius hemoglobins and thus seems less pliable to phosphate-mediated variation in oxygen affinity. The data are discussed in relation to the hemoglobin systems of other fish.
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PMID:Oxygen-binding properties of hemoglobins from estivating and active African lungfish. 1 21

1. The rate of volume flow across frog skin induced by an osmotic gradient was measured when normal (7.4) and low pH (2.28) solutions bathed the outside. The osmotic permeabilities (Pos) were 2.4 +/- 0.4 and 4.8 +/- 1.0 micrometer/sec, respectively. The change in Pos induced by low pH was reversible. 2. Volume flow in the absence of an osmotic gradient was measured at normal and low pH. Values were 0.69 +/- 0.13 and 1.1 +/- 0.2 microliter/hr. cm2, respectively; the paired differences were significant (P less than 0.0025). This change in rate was partially reversible upon return to normal pH. 3. The potential difference (V) and short-circuit current (Is) across skins were measured under several conditions and the following equivalent parameters in a simplified electrical model were computed: total resistance (Rt); shunt resistance (Rs); electromotive force of the pump (ENa); and salt transport at open circuit (JNaCl). Representative figures were (a), at pH 7.4: Is = 14 +/- 1.6 microampere/cm2; Rt = 3.3 +/- 0.4 komega.cm2; Rs = 7.2 +/- 1.0 komega.cm2; ENA = 103 +/- 38 mV; JNaCl = 7.2 +/- 1.2 microampere/cm2; (b) at pH 2.28: Is = 8.3 +/- 2.1 microampere/cm2; Rt = 0.46 +/- 0.12 komega. cm2; Rs = 0.65 +/- 0.06 komega.cm2; ENa = 59 +/- 25 mV; JNaCl = 9.4 +/- 3.3 microampere/cm2. 4. From the electrical parameters measured concomitantly with the rate of fluid transport in given experiments, the expected salt concentration of the transported fluid was 0.30 +/- 0.08 and 0.38 +/- 0.08 mole/l. at normal and low pH, respectively, or some 3-4 times hyperosmotic with respect to the medium. 5. Treatment with low pH on the outside has been found to open the intercellular junctions in previous studies. The present results suggest that, if such an effect occurs, it is localized only to a small fraction of the cell perimeter. Making certain assumptions that fraction could be as low as 0.003. 6. Low pH on the outside reversibly changes the electrical parameters of a 'tight' epithelium like the frog skin into values more typical of 'intermediate' epithelia; both the total and shunt resistances decrease to about 0.1 of their normal values. These changes do not apparently affect the osmolarity of the transported fluid.
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PMID:The effect of external pH on osmotic permeability, ion and fluid transport across isolated frog skin. 2 37

The kinetics of degradation of cefazolin and cephalexin in aqueous solution were investigated at 60 degrees C and constant ionic strength over the entire pH range. The observed degradation rates were obtained by measuring the residual cephalosporin and were shown to follow pseudo-first-order-kinetics. They were influenced significantly by solvolytic and hydroxide ion catalysis. No primary salt effect was observed in the acid or basic pH region. Of the buffer systems employed in the kinetics studies only the phosphate buffer system showed a catalytic effect. The pH-rate profile for cefazolin showed a degradation minimum between pH 5.5 and 6.5. Cephalexin did not show a pH minimum in that region. The apparent energies of activation were determined for cefazolin and cephalexin at pH 5.5 and were calculated to be 24.3 Kcal/mole and 26.2 Kcal/mole, respectively. The agreement between the calculated theoretical pH-rate profiles and the experimental points for both compounds support the hypothesis presented concerning the reactions involved in their respective degradation pathways.
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PMID:Kinetics of degradation of cefazolin and cephalexin in aqueous solution. 3 81

The degradation kinetics of a new cephalosporin derivative (1) in aqueous solution were investigated at 60 degrees, mu = 0.05, at pH 2.0-10.0. The observed degradation rates followed pseudo-first-order kinetics and were influenced significantly by H2O and OH- catalysis. No primary salt effect was observed in the acid region, but a positive salt effect was observed at pH 9.4. A general base catalytic effect by a phosphate buffer species was observed at pH 7-8. The pH-rate profile for I exhibited a degradation minimum at pH 6.05. The Arrhenius activation energies determined at pH 4.0 and 9.4 were 27.2 and 24.5 kcal/mole, respectively. Excellent agreement between the theoretical pH-rate profile and the experimental data supported the hypothesized degradation process. A comparison of I and cefazolin revealed close structural and stability analogies.
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PMID:Degradation kinetics of a new cephalosporin derivative in aqueous solution. 4 33

Phytase was purified from Aspergillus niger culture fluid by molecular sieve filtration on Sephadex G-200, followed by thermal inactivation of acid phosphatase and CM-cellulose chromatography. The 12-fold purified enzyme had two pH optima at 2.7 and 5.5 and was characterized by high thermal stability in alkaline environment and broad substrate specificity. The Michaelis constant of phytase relative to myo-inositol hexaphosphate sodium salt is 4.8 X 10(-4) M and activation energy 9,217 cal/mole. The molecular weight of the enzyme is estimated at 200,000.
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PMID:Some properties of partially purified phytase from Aspergillus niger. 7 23

When closed circular SV40 DNA containing 58 negative superhelical turns is used as a template for RNA synthesis with Escherichia coli RNA polymerase, a fraction of the RNA product remains complexed with the DNA. The RNA in the complex is resistant to ribonuclease in high salt, and the Tm indicates that it is hydrogen bonded to the DNA. The mole ratio of RNA to DNA nucleotides in the complex ranges from 0.01 to 0.08; the RNA ranges in length from 80 to 600 nucleotides. The formation of the complex is dependent on the circular DNA being topologically underwound since no complex is formed when closed circular DNA containing zero superhelical turns is used as the template. The DNA-RNA complex can serve as a primer-template combination for in vitro DNA synthesis by E. coli DNA polymerase I. After synthesis with (alpha-32P)-labeled deoxyribonucleoside triphosphates followed by alkaline hydrolysis, the isolation of 32P-labeled ribonucleotides is evidence for a covalent linkage between the RNA and the DNA synthesized. During the in vitro DNA synthesis, the template is nicked at a low rate, and the nicked molecules support extensive DNA synthesis. This observation indicates that only limited synthesis can occur on unnicked molecules possibly owing to the topological constraints against unwinding of the helix. Possible models for in vivo priming of double-stranded DNA by E. coli RNA polymerase are discussed.
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PMID:Priming of superhelical SV40 DNA by Escherichia coli RNA polymerase for in vitro DNA synthesis. 16 2

1. The hydrolysis of guanosine triphosphate (GTP) and the consequent formation of guanosine diphosphate (GDP) and phosphate (P1) are activated by light in a suspension of broken retinal rods: the hydrolysis rate with GTP in the micrometer concentration range is 2.5-3.5 n-mole/min per mg of rhodopsin in the preparation. 2. The ionic composition of the medium suspending the rods is not critical: the hydrolysis is present in NaCl saline solution with MG2+ as well as in Tris-HC1 buffer solution, and with the chelating agent EDTA. 3. The ionic strength is critical: the effect is reduced when the broken rods are suspended in a low salt mannitol solution, and is altogether abolished when they are separated from the mannitol solution; it reappears when the mannitol solution is added again in the presence of salts. An element essential for the effect is thus reversibly released in the mannitol solution. No hydrolytic activity on GTP, however, is found in the mannitol soluble fraction. 4. The cyclic nucleotide phosphodiesterase is eluted from the rods in the mannitol solution, and is reaggregated to the rods in the presence of salts; once recombined with the rods, it can be activated by light. 5. The activation of the phosphodiesterase by light is present in the absence of added nucleotide triphosphates.
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PMID:Light-activated hydrolysis of GTP and cyclic GMP in the rod outer segments. 20 80

When myofibrils from rat hearts were dissolved in concentrated salt solutions and reprecipitated by dilution, they contained both protein kinase (partly cyclic 3':5'-AMP-dependent) and protein phosphatase activities. Troponin-I was the major protein to be phosphorylated by the endogenous myofibril-associated kinase and by added protein kinase. Approximately 1 mole of phosphate per mole of troponin-I was incorporated from radioactive ATP, but the extent of troponin-I phosphorylation could be varied experimentally. An inverse correlation was found between protein phosphorylation and the maximum Ca2+-stimulated myofibrillar Mg2+-ATPase activity, while the amout of calcium required for half-maximum activation was proportional to the extent of protein phosphorylation. The changes in Mg2+-ATPase activity produced in vitro by protein phosphorylation were reproduced in isolated perfused rat hearts treated for short periods with L-noradrenaline (10(-6)M). The changes in myofibrillar function brought about as the result of the phosphorlyation by cAMP-dependent protein kinase suggest that the contractile response is desensitized in order to cope with the rise in intracellular Ca2+ which results from the action of catecholamines on cardiac ventricular cells.
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PMID:Cardiac myofibrillar phosphorylation and adenosine triphosphatase activity. 22 75


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