PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Countercurrent Distribution”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 235 records · Page 13Linked to original sources
PubMed1978

[Method of partitioning polyene macrolide antibiotics].

Levorin and mycoheptin, polyenic antibiotics were separated into 3 and 7 heptaenic components respectively by the method of disc electrophoresis in 7.5 per cent polyacryl amide gel prepared with tris-HCl buffer, pH 8.9. It was shown that nystatin had different composition as dependent on the organism producing it. The results of electrophoresis confirmed the data of the counter-current distribution.

Antifungal Agents↗
PubMed1984

Effect of sample dilution on measurements of free (unbound) hormones.

We describe the influence of sample dilution on the measurement of free or non-protein-bound hormones in serum or plasma. The concentration of free hormone in the sample will alter after dilution or addition of binding reagents. The extent of this equilibrium perturbation depends on the binding properties of the endogenous carrier proteins, which vary from sample to sample and from sample to reference standard. As examples, we demonstrate the different changes in concentrations of free thyroxin and free cortisol after dilution, both experimentally and by theoretical modeling of the hormone-protein distribution. We also show how this systematic error can be minimized in the design of free hormone assays.

Carrier Proteins↗
PubMed1992

Surface heterogeneity of rat sperm during maturation.

Rat sperm isolated from the caput and caudal epididymis and the vas deferens were subjected to multiple partition in aqueous two-phase systems. The technique was used to reveal heterogeneity of a sperm population with respect to particular surface properties. Sperm from all three regions gave broad distributions indicative of heterogeneous cell populations. Greatest heterogeneity was observed for cauda sperm with caput and vas sperm producing similar distributions. Following multiple partition sperm from different regions of the distribution profiles were immunostained with three antibodies known to recognise maturation antigens. The results show that some antigens are acquired during epididymal transit whilst others are present throughout. The partition (surface heterogeneity) seen cannot therefore be explained solely by the distribution of the antigens recognized by 2D6, 6B2 and 3D5.

Animals↗
PubMed1994

Effect of some poly(ethylene glycol)-bound and dextran-bound affinity ligands on the partition of synaptic membranes in aqueous two-phase systems.

Ligands with an apparent affinity for various structural elements on the surface of synaptic membrane fragments have been bound to the polymers poly(ethylene glycol) and dextran. The ligand-polymer derivatives have been included in aqueous two-phase systems composed of water, poly(ethylene glycol) and dextran. The uneven distribution of the polymers resulted in the concentration of the polymer-bound ligand in one of the two phases. The effect of the ligand-polymer on the partition of membranes was studied by using synaptic membranes from calf brain, obtained by standard centrifugation methods. By using ligand-containing two-phase systems for nine-step counter-current distribution of membranes, it was shown that the distribution behaviour of various parts of the membrane preparation could be affected. The distribution was followed by determination of opiate binding, acetylcholinesterase, and total membrane (using protein and light-scattering measurements).

Acetylcholinesterase↗
PubMed1984

Liquid-liquid extraction of membranes from calf brain using conventional and centrifugal counter-current distribution techniques.

Neural membranes isolated from calf brain have been partitioned in aqueous two-phase systems containing dextran and polyethyleneglycol. When the partition was repeated several times, using counter-current distribution technique, the distribution of the membranes between the upper phase and the interface changed in a non-ideal manner and in favour of the interface. By using a centrifugal counter-current distribution device the time for the experiment could be reduced by a factor of 7-8 and the distribution was similar to what could be expected for ideally behaving membranes. The time-dependent change of the membranes is discussed in terms of aggregation and lateral membrane perturbations. Despite this effect a certain fractionation has been achieved as deduced from analysis of cholesterol content, opiate receptor activity and acetylcholinesterase activity along the counter-current distribution row of fractions. Compared to the starting material these activities were enriched some two-fold in certain fractions.

Animals↗
PubMed1988

Lateral heterogeneity of rat liver plasma membranes analysed by counter-current distribution.

The lateral heterogeneity of rat liver plasma membranes was examined by fragmentation and fractionation by counter-current distribution in an aqueous two-phase polymer system. The distribution pattern was analysed by plotting the relative specific activities of marker components against each other. By this analysis asialo-orosomucoid receptors were found in a domain separated from domains containing 5'-nucleotidase and leucine aminopeptidase by another domain devoid of these markers. 5'Nucleotidase and leucine aminopeptidase resided in adjacent but separate domains. The experimental data were compared with corresponding plots of markers in model membranes. The model membranes yielded plots of different shapes depending on marker distribution and fragment size. This method of analysis should be useful for examining the lateral heterogeneity also of other membranes.

5'-Nucleotidase↗
PubMed1988

Partition and counter-current distribution of membrane particles in aqueous dextran-poly(ethylene glycol) two-phase systems with special reference to synaptosomes.

Aqueous two-phase systems composed of water, dextran and poly(ethylene glycol) can be used for the separation of biological particles. The adjustment of the partition of such particles between the two phases and the interface between them has been studied by using a preparation of synaptosomes (from calf brain cortex) also containing free mitochondria. The partition has been affected by variation of polymer concentrations and addition of salts, e.g. phosphates and chloride. The time for separation of the phases showed a bimodal behaviour with an initially rapid formation of bulk phases followed by a slow phase separation. The relative amount of mixed phases at the time of the transition was proportional to the amount of particles included. Counter-current distribution with moderate time for the phase separation was carried out in such way that the interface material travelled with approximately half the speed of the moving upper phase. In this way the distribution of the particles between the upper phase and the interface as well as between the interface and the lower phase could be studied in the same experiment. The heterogeneity of the synaptosome preparation was clearly demonstrated by counter-current distribution at low polymer concentrations while no separation was obtained when the system contained larger amounts of polymers. Possible reasons for this behaviour are discussed.

Animals↗
PubMed1992

Rat bone marrow erythroid cell fractionation by counter current distribution in non-charge-sensitive two-phase systems.

Counter-current distribution in non charge-sensitive aqueous poly(ethylene glycol)-dextran two phase systems allows the fractionation of rat bone marrow cells into two broad cell subpopulations with different distribution coefficients in a relatively short time. Morphological identification and enzymatic studies suggest that erythroid cells are mainly present in the subpopulation with the higher distribution coefficient. The distribution coefficient and, therefore, surface hydrophobicity of these cells, apparently increase in parallel with an increase in their degree of differentiation and maturation.

Animals↗
PubMed1989

Heterogeneity of smooth endoplasmic reticulum from rat liver studied by two-phase partitioning.

Smooth microsomal membranes, prepared from rat liver by sucrose-density-gradient centrifugation, were subfractionated by counter-current distribution in an aqueous two-phase system consisting of poly(ethylene glycol) and Dextran T500. A comparison of the distribution curves of marker enzymes, together with theoretically calculated curves, indicated the presence of at least five membrane subfractions, differing in the ratios of the marker enzymes. Glucose-6-phosphatase and arylesterase distributed in one manner, and NADPH-cytochrome c reductase and NADH-ferricyanide reductase in another. Evidence for further heterogeneities in the distribution of marker enzymes in smooth microsomes was obtained by analysing the membrane domain structure using a recently described method [Albertsson (1988) Q. Rev. Biophys. 21, 61-98]. Phenobarbital treatment did not influence the behaviour of the marker enzymes.

Animals↗
PubMed1985

Studies on the ATP-sensitivity of yeast phosphofructokinase by means of affinity partitioning using polymer bound Cibacron blue F3G-A.

Yeast phosphofructokinase was partitioned in an aqueous two-phase system composed of polyethylene glycol and dextran in which a small amount of the first polymer was replaced by Cibacron Blue F3G-A substituted polyethylene glycol. It was found that the partition coefficient, K, of the enzyme determined immediately after adding the enzyme to the system and within a series of time intervals (min) shifts from a lower to a higher value. This effect was amplified when the enzyme was preincubated with fructose 6-phosphate in millimolar concentration range. Other effectors, like ATP, ADP, AMP, fructose 1,6-bisphosphate and protons were without significant influence on the partition. A similar behaviour in lowering the partition coefficient was found with an enzyme form desensitized to ATP-inhibition. The existence of enzyme forms of different affinity to Cibacron Blue depending on the fructose 6-phosphate could be manifested by counter-current distribution. Because of the competition in the binding of Cibacron Blue and ATP to the nucleotide binding sites the conclusion was drawn that the partition of phosphofructokinase reflects the alteration of the affinity of the enzyme to ATP.

Adenosine Triphosphate↗
PubMed1969

Lipid metabolites of carbon tetrachloride.

5 min after intravenous injection into rats of (14)C- or (36)Cl-carbon tetrachloride, liver lipids were found labeled. Most of the radioactivity was found in the phospholipid fraction. The metabolites were shown to comprise a heterogeneous group of branched long-chain chlorinated fatty acids, probably containing the trichloromethyl side chain. Surviving liver slices also formed these metabolites. In a simple chemical system which generates trichloromethyl free radicals, carbon tetrachloride added to methyl oleate to form esters which behaved like the metabolites during counter-current distribution and urea adduction. The evidence strongly suggests the formation of these metabolites by free radical attack on unsaturated lipids. The relation of these observations to current theories of carbon tetrachloride intoxication is discussed.

Animals↗
PubMed1990

Fractionation in two-phase systems of red cells during rat development: changes in pyruvate kinase and bisphosphoglycerate mutase activities in relation to red cell switching.

An inverse relationship between 2,3-bisphosphoglycerate levels and the ratio calculated from pyruvate kinase and bisphosphoglycerate mutase activities has been observed in red populations of rats during animal development. Counter-current distribution in aqueous two-phase systems of these cells populations shows a displacement of distribution profiles towards the high-numbered cavities of the rotor as animal ages. Heterogeneity of cells after distribution is only observed during the switching process from fetal to adult red cells taking place along the postnatal stage of development. Values for the pyruvate kinase/bisphosphoglycerate mutase ratio in these fractions suggest the separation of fetal (liver) from adult (bone marrow) red cells.

Animals↗