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

1. The permeability of human red cells to (36)Cl(-) and to [(35)S]SO(4) (2-) was studied in the presence of various monovalent anions.2. A maximum decrease of anion permeability was found in a study of the steady-state exchange of (36)Cl in a medium containing 120 mM salicylate. The exchange had a half-time of 3 hr at 0 degrees C, a reduction of normal chloride permeability by a factor of 10(5). The activation energy of chloride exchange decreased from a value of 45 to 22 kcal/mole in the interval between 0 and 10 degrees C. Simultaneous determination of the permeability to potassium and chloride proved that salicylate induced a reversal of the normal selectivity of red cells at 0 degrees C (permeability coefficient P(K) of 3.5 x 10(-9) cm/sec to be compared with a P(Cl) of 2 x 10(-9) cm/sec).3. In contradistinction to the slow movement of (36)Cl, the exchange of [(14)C]salicylate was completed within 4 min, when red cells were suspended at 0 degrees C in the salicylate medium.4. A study of the sulphate permeability at 38 degrees C showed that the rate of steady-state exchange decreased, when chloride was replaced by lyotropic anions other than bromide. The sequence of the permeability decrease was: Cl(-) = Br(-) < I(-) < NO(3) < SCN(-) < salicylate, the same sequence which previously has been shown to increase the permeability to sodium and potassium. The activation energies of sulphate exchange were 32 kcal/mole (chloride medium), and 38 kcal/mole (thiocyanate medium).5. Sufficient data were obtained during the study to demonstrate that when equilibrium has been obtained, there is a good agreement between the values of (36)Cl (cell water)/(36)Cl (extracellular water) and of {[(35)S]SO(4) (cell water)/[(35)S]SO(4) (extracellular water)}((1/2)).6. It is concluded that the anion-induced changes of permeability are due to binding of anions to fixed cationic charges in the red cell membrane.
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PMID:Effect of some monovalent anions on chloride and sulphate permeability of human red cells. 549 37

Conformational energy calculations have been performed on butaclamol and isobutaclamol using Allinger's MM2 (Molecular Mechanics II) program. Cis arrangements of rings D and E were found to be preferred by 1.4-1.9 kcal/mole for both compounds. Nevertheless, based on a molecular comparison with a number of semirigid neuroleptics, most notably loxapine and octoclothepin, it is suggested that trans arrangements are required for neuroleptic activity in the two compounds. However, trans conformer B of butaclamol, which was previously postulated as the biologically active form, was found to be 4.1 kcal/mole higher in energy, suggesting that it is less likely to play a significant pharmacological role. The biologically active forms are identified as trans conformer A for butaclamol and trans conformer B for isobutaclamol. Certain regularities in the structures of the semirigid neuroleptics are noted. It is also speculated that the cis conformers of protonated butaclamol may have unfavorable geometries for ion solvation, which would account for the anomalously low pKa measured for the compound. A similar explanation would also account for a trans conformer being found in the crystal structures of the bromide salts of butaclamol and dexaclamol.
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PMID:Conformational properties of butaclamol and isobutaclamol. Regularities in the structures of semirigid neuroleptics. 619 5

Chromatin from two human colon adenocarcinoma cell lines (HT-29 and LoVo) showed similar digestion kinetics when sensitivities to DNase I and micrococcal nuclease were examined. Chromatin conformations were probed by examining the binding of ethidium bromide. A Scatchard plot revealed that both chromatins bound the same amount of ethidium bromide per mole of DNA, but the DNA from LoVo cells was more accessible to the intercalator. The results indicate that differences in chromatin conformation are not necessarily accompanied by different nuclease sensitivities.
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PMID:Two human colon tumor cell lines with similar nuclease sensitivities have different ethidium bromide binding characteristics. 623 36

1. Binding of a purified scorpion toxin to membrane fragments isolated from electroplaque of an electric eel Electrophorus electricus was studied using a radio-iodinated toxin.2. A scorpion toxin was purified from the venom of Leiurus quinquestriatus and iodinated with (125)I in a lactoperoxidase-catalysed reaction. Monoiodinated toxin, isolated by an ion exchange chromatography, retarded the inactivation kinetics of Na current to a similar extent as the native toxin, indicating that radioiodination did not appreciably affect physiological and binding properties of the native toxin.3. Analyses of binding properties by Scatchard plots showed the presence of two classes of binding sites (with low and high affinities) in the membrane preparation from eel electroplaque; similar preparation from an electric skate, of which the electroplaque is known to be devoid of Na channels, possessed only the low affinity sites.4. The number of high affinity sites in the eel preparation was 41.8 +/- 10.5 p-mole/g tissue; the value was within the range reported for tetrodotoxin binding to similar preparations (15-148 p-mole/g tissue).5. A variety of cations (Na(+), Mn(2+) and La(3+)) inhibited the high affinity scorpion toxin binding, as indicated for the toxin binding to Na channels by a previous electrophysiological study. K(D) value in the presence of 120 mM-Na(+) (approx. 8 nM) agreed reasonably with that (approx. 10nM) reported for the scorpion toxin binding to excitable neuroblastoma cells or synaptic nerve ending particles under conditions where membrane potential was depolarized by the addition of 135 mM-KCl.6. Pretreatment of the eel membrane preparation with beta-bungarotoxin (7-44 ng/ml.) in the presence of Ca ions (10-200 muM) resulted in a substantial loss of high affinity binding of scorpion toxin. When phospholipase A(2) activity of the beta-toxin was inactivated by a chemical modification with p-bromophenacyl bromide, the inhibitory action of the beta-bungarotoxin was abolished.7. It is concluded that a high affinity binding of scorpion toxin to the eel electroplaque membrane fragments represents the binding to Na channels in vitro, and that phospholipase A(2) activity of beta-bungarotoxin interferes with the binding of scorpion toxin to Na channels.
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PMID:Binding of scorpion toxin to sodium channels in vitro and its modification by beta-bungarotoxin. 624 82

The effects of external anions on gating of Na channels of frog skeletal muscle were studied under voltage clamp. Anions reversibly shift the voltage dependence of peak sodium permeability and of steady state sodium inactivation towards more negative potentials in the sequence: methanesulfonate less than or equal to Cl- less than or equal to acetate less than Br- less than or equal to NO-3 less than or equal to SO2-4 less than benzenesulfonate less than SCN- less than ClO-4; approximately the lyotropic sequence. Voltage shifts are graded with mole fraction in mixtures and are roughly additive to calcium shifts. The peak PNa is not greatly affected. Except for SO2-4, these anions did not change the Ca++ activity of the solutions as measured with the dye murexide. Shifts of gating can be explained as the electrostatic effect of anion adsorption to the Na channel or to nearby lipid. Such adsorption is expected to follow the lyotropic series. Anions also interfere significantly with the response of a Ca-sensitive membrane electrode following the same sequence of effectiveness as the shifts of gating. The lyotropic anions decrease the Ca++ sensitivity and cause anomalously negative responses of the Ca electrode because these anions are somewhat permeant in the hydrophobic detector membrane.
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PMID:Lyotropic anions. Na channel gating and Ca electrode response. 630 98

A new apolipoprotein E (apo E) phenotype has been demonstrated in a Finnish hypertriglyceridemic subject (R.M.). At the time of this study, R.M.'s plasma triglyceride and cholesterol levels were 1,021 and 230 mg/dl, respectively. The subject's apo E isoelectric focusing pattern was characterized by two major bands, one in the E3 position and the other in the E1 position. Normally the E1 position is occupied by sialylated derivatives of apo E4, E3, or E2. The E1 band of subject R.M. is not a sialylated form, however, because it was not affected by neuraminidase digestion. The identity of the E1 variant as a genetically determined structure was established by amino acid and partial sequence analyses, confirming that the variant is an example of a previously uncharacterized apo E phenotype, E3/1. Both cysteamine modification and amino acid analysis demonstrated that this variant contains two cysteine residues per mole. Sequence analysis of two cyanogen bromide fragments and one tryptic fragment of the apo E3/1 showed that it differs from E2(Arg158----Cys) at residue 127, where an aspartic acid residue is substituted for glycine. This single amino acid interchange is sufficient to account for the one-charge difference observed on isoelectric focusing gels between E2(Arg158----Cys) and the E1 variant. The variant has been designated E1 (Gly127----Asp, Arg158----Cys). When compared with apo E3, the E1 variant demonstrated reduced ability to compete with 125I-LDL for binding to LDL (apo B,E) receptors on cultured fibroblasts (approximately 4% of the amount of binding of apo E3). This defective binding is similar to that of E2-(Arg158----Cys). Therefore, the binding defect of the variant is probably due to the presence of cysteine at residue 158, rather than aspartic acid at residue 127. In contrast, the apo E3 isoform from this subject demonstrated normal binding activity, indicating that it has a normal structure. In family studies, the vertical transmission of the apo E1 variant has been established. It is not yet clear, however, if the hypertriglyceridemia observed in the proband is associated with the presence of the E1(Gly127----Asp, Arg158----Cys) variant.
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PMID:A novel electrophoretic variant of human apolipoprotein E. Identification and characterization of apolipoprotein E1. 632 33

We have purified propionyl-CoA carboxylase from normal, postmortem human liver to homogeneity. The isolation procedure, which provided an approximately 3000-fold purification and an overall yield of 26%, employed initial centrifugation of a cetyltrimethylammonium bromide-treated homogenate, followed by sequential chromatographic separations using DEAE-cellulose, Blue Sepharose, and Bio-Gel A-1.5m. The native enzyme has a molecular weight of approximately 540,000 and is composed of nonidentical subunits (alpha and beta) of Mr = 72,000 and 56,000, respectively. When studied with analytical isoelectrofocusing techniques, it focuses as a single peak at pH 5.5. Each mole of native enzyme contains 4 mol of bound biotin, virtually all of which is found with the larger (alpha) subunit. The apparent Km values for ATP, propionyl-CoA, and bicarbonate are 0.08 mM, 0.29 mM, and 3.0 mM, respectively. The enzyme also catalyzes the carboxylation of acetyl-CoA and butyryl-CoA to a limited degree, but not that of crotonyl-CoA. Propionyl-CoA carboxylase is quite stable over a temperature range from -50--37 degrees C and over a pH range from 6.2 to 8.4. It has a broad pH optimum from pH 7.2 to 8.8. Limited proteolysis with trypsin results in slow, time-dependent deactivation of the enzyme with preferential cleavage of the smaller subunit. Antiserum prepared against the native enzyme is shown to be monospecific by immunodiffusion and immunoelectrophoresis.
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PMID:Isolation and characterization of propionyl-CoA carboxylase from normal human liver. Evidence for a protomeric tetramer of nonidentical subunits. 676 47

Carbonic anhydrase (EC 4.2.1.1) has been purified from the erythrocytes of the tammar wallaby (Macropus eugenii desmarest). The enzyme was separated into four zones of activity. The three major individual forms were isolated as discrete entities. Comparison of substrate specificity, specific activities, kinetic constants and inhibition characteristics indicated that these heteromorphs represented minor post-translational modifications of a single gene product of carbonic anhydrase II type. Double-immunodiffusion and peptide mapping confirmed this proposition. The marsupial enzyme exists as a monomer with a molecular weight of about 29 000 containing one atom of zinc per mole which is much more tightly bound to the enzyme than it is in either human carbonic anhydrase I or II. The wallaby enzyme was, like human carbonic anhydrase II, partially inactivated by p-hydroxymercuribenzoate under conditions not inhibitory for human carbonic anhydrase I. The partial sequence of 51 residues of cyanogen-bromide peptides was sufficiently homologous to allow unambiguous overlap with the sequence of both human carbonic anhydrase I and II isozymes as well as with the recently published sequence of an apparent type I-like enzyme from the turtle. It is clear that the single wallaby erythrocyte carbonic anhydrase belongs to the class of separately evolving type II isozymes which have previously been defined only for placental mammals.
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PMID:Purification, properties, partial sequence and evolutionary relationships of marsupial erythrocyte carbonic anhydrase. 681 2

A new method for preparing fluorescein derivatives of polysaccharides is described. These derivatives are prepared by activation of the polysaccharide with cyanogen bromide and subsequent reaction with fluoresceinamine. The optimum conditions for coupling have been established in this report. Using this procedure, we have prepared fluorescein derivatives of a wide variety of polysaccharides. Degrees of substitution in the range of 3.0 X 10(-3) to 2.4 X 10(-2) mol of fluorescein per mole of monosaccharide equivalent were obtained. The fluorescent derivatives are stable: no free fluorescein was detected after incubation at 22 degrees C for 48 h or at -10 degrees C for 4 months. The fluorescein-derivatized polysaccharides were found to have the same potency in inhibiting lectin-mediated hemagglutination as the underivatized polysaccharide. In addition, these fluorescent polysaccharides can be radioiodinated to specific activities exceeding 10(6) dpm/micrograms due to incorporation of 125I into fluorescein. The cell binding properties of 125I-fucoidin and 125I-heparin are indistinguishable from the corresponding underivatized polysaccharides. This general approach for preparing fluorescent polysaccharides should produce useful reagents for localizing and quantifying cell surface carbohydrate-binding proteins (lectins).
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PMID:Preparation and properties of fluorescent polysaccharides. 686 15

Pig heart aconitase reacts with one mole of phenacyl bromide per molecule to give complete inactivation due to the alkylation of a cysteine reside at the active site. A tryptic peptide containing this essential residue has been isolated and its amino acid sequence determined at Ile-Gln-Leu-Leu-Cys *-Pro-Leu-Leu-Asn-Gln-Phe-Asp-Lys by manual methods and by the use of an automated solid phase sequencer. There is a limited similarity in amino acid sequence between this peptide and other peptides containing the cysteine residues involved in the binding of the iron-sulfur clusters of high-potential iron-sulfur protein of Rhodopseudomonas gelatinosa and rubredoxins from various bacteria.
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PMID:Amino acid sequence of a peptide containing an essential cysteine residue of pig heart aconitase. 721 10


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