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At least 379 records · Page 21Linked to original sources
PubMed1990

High-performance liquid chromatographic separation and dual competitive binding assay of corrinoids in biological material.

Corrinoids were extracted with hot ethanol from human plasma and faeces and separated by high-performance liquid chromatography. The corrinoids (cobalamin and cobalamin analogues) were quantified in the eluted fractions by a dual radioisotope assay using as binders intrinsic factor and haptocorrin to detect cobalamin and total corrinoids, respectively. Recoveries ranged from 37.7 +/- 5.1% for hydroxycobalamin to 75.0 +/- 9.1% for cyanocobalamin. In plasma, the main forms of cobalamin were the coenzymes methylcobalamin and 5'-deoxyadenosylcobalamin (32.1 +/- 13.4 and 28.4 +/- 12.3%, respectively, of total corrinoids). The cobalamin analogue fraction of plasma was eluted with a retention time close to that of cobinamide and of deoxyadenosylcobalamin. In the faeces, most of the corrinoids separated were detected better by the haptocorrin assay than by the intrinsic factor assay. One corrinoid peak was eluted with the same retention time as cobinamide. This peak was detected by haptocorrin assay but not by intrinsic factor assay. It could therefore correspond to cobinamide.

Chromatography, High Pressure Liquid↗
PubMed1998

Competitive binding assay for thyroxine using in vitro selected oligonucleotides.

A new binding assay that uses oligodeoxyribonucleotides (DNAs) obtained by the in vitro selection method, instead of antibodies, to bind to the target molecule, thyroxine (T4), is described. The DNAs which selectively bound to the T4 were selected, labeled with biotin or radioisotope, and then used to detection of T4 in the presence of liothyronine (T3), which has a chemical structure similar to that of T4.

Biosensing Techniques↗
PubMed2005

Surface-enhanced Raman spectroscopy as a probe of competitive binding by anions to citrate-reduced silver colloids.

Citrate-reduced silver colloids (CRSCs) are used extensively for surface-enhanced Raman scattering (SERS) studies of cations but are typically found to be ineffective for detection of anions unless they are treated with compounds that give them positively charged coatings. In this work CRSCs which were suitable for detection of anions were generated by treatment with aggregating agents that did not bind strongly to the silver surface. Under these conditions the major factor determining the enhancement of added anions was their ability to displace whatever anions were already present. In the case of CRSCs, residual citrate was observed when the colloids were aggregated with sulfate salts, since neither sulfate nor the residual nitrate displaced it. On addition of more strongly binding anions, such as halides, the citrate was displaced and the bands of the added analyte appeared, allowing them to be detected without the need for creation of positively charged coatings. It was found that the relative affinities of the anions, as determined by displacement experiments monitored by SERS, followed the solubilities of their silver salts, presumably because both properties are strongly dependent on the strength of the Ag-anion bonds. The relative affinities determine which anions can be detected in the presence of which others; nitrate, sulfate, and perchlorate are lower in the series than citrate and so are not observed. Displacement experiments show that dipicolinic acid (DPA) and Cl(-) have similar (stronger) binding, but they can be displaced in turn by Br(-) and I(-), which have the highest affinity and lowest solubility. This model allows a broad range of previous observations to be rationalized and allows the experimental conditions suitable for detection of particular new analytes to be designed on rational principles.

Journal Article↗
PubMed1972

Competitive binding of somatomedin to the insulin receptors of adipocytes, chondrocytes, and liver membranes.

The action of growth hormone on skeletal tissue is mediated through somatomedin, a low molecular weight peptide found in serum. This peptide, formerly known as "sulfation factor" or "thymidine factor," produces marked insulin-like effects in various target tissues. Since at least some of the metabolic effects of insulin on target cells are initiated by a highly specific interaction with receptors on cell membranes, this study was undertaken to determine whether somatomedin might interact with the same binding sites. It was found that somatomedin, at physiological concentrations, competes with (125)I-labeled insulin for receptor sites on isolated fat cells, liver membranes, and isolated chondrocytes, and that the relative binding affinities of insulin and somatomedin reflect the in vitro biological potencies of the two hormones in these tissues. This is the first demonstration of a peptide other than insulin, proinsulin, or derivatives of insulin competing for insulin-binding sites, and implies a structural, as well as a functional, homology between somatomedin and insulin. Somatomedin may be only one of a larger group of homologous pleiotypic peptides with different target organ specificities.

Adipose Tissue↗
PubMed2003

Competitive binding of Pu and Am with bone mineral and novel chelating agents.

Effective direct removal of actinides such as Pu and Am from bone in vivo has not been accomplished to date, even with the strong chelating agents CaNa3DTPA or ZnNa3DTPA. This study, using an established in vitro system, compared removal of Pu and Am bound to bone mineral by ZnNa3DTPA and 10 chelating agents designed specifically to sequester actinides, including Pu and Am. Ligands tested were tetra, hexa, and octadentate, with linear or branched backbones containing sulfocatechol [CAM(S)], hydroxycatechol [CAM(C)], hydroxipyridinone (1,2-HOPO, Me-3,2-HOPO), or hydroxamate functional groups. The wide range of Pu and Am removal exhibited by the test ligands generally agreed with their metal coordination and chemical properties. The most effective agents for Pu (100 microM concentration, 24-48 h contact) are all octadentate as follows: 3,4,3-LICAM(S) (54% unbound); 3,4,3-LICAM(C) (6.2%); 3,4,3-LI(1,2-HOPO) (3.8%); H(2,2)-(Me-3,2-HOPO) (2.2%) and DFO-(1,2-HOPO) (1.8%). The other ligands removed less than 1% of the bound Pu; and ZnNa3DTPA removed only 0.086%. The most effective ligands for Am removal (100 microM, 24-48 h contact) are as follows: octadentate H(2,2)-(Me-3,2-HOPO) (21% unbound); 3,4,3-LI(1,2-HOPO) (14.5%) and 3,4,3-LICAM(C) (5.9%); hexadentate TREN-(Me-3,2-HOPO) and TREN-(1,2-HOPO) (9.6%); and tetradentate 5-LIO(Me-3,2-HOPO) (5.2%). Am removal by ZnNa3DTPA was about 1.4%. Among the ligands presently considered for possible human use, only 3,4,3-LI(1,2-HOPO) removed potentially useful amounts of both Pu and Am from bone mineral.

Americium↗