Binding Of Rabbit Research Articles

The motilin pharmacophore in CHO cells expressing the human motilin receptor

We performed a structure–activity study with the human motilin receptor, which was recently cloned from thyroid tissue. N-terminal fragments, Ala-analogs of motilin, and motilides were tested in a cell line that expresses the cloned human motilin receptor and apoaequorin. Full potency to induce calcium fluxes was obtained with N-terminal fragments of 14 amino acids. Motilin fragments 1–14 in which residues 1 (Phe), 4 (Ile), and 7 (Tyr) were replaced by Ala showed the largest reduction in potency. Only motilides with an enol configuration had markedly higher potencies compared to erythromycin A. The potencies to induce Ca 2+ fluxes correlated strongly with rabbit binding and contractility data, suggesting that the cloned receptor is indeed the motilin receptor, responsible for contractile effects. Conservation of the motilin pharmacophore in evolution indicates an important physiological role of motilin.

Binding and intracellular fate of beta-very low density lipoprotein in isolated rat liver parenchymal cells.

Binding of rabbit 125I-tyramine-cellobiose-beta-very low density lipoprotein (125ITC-beta-VLDL) was saturable both in suspended and cultured rat liver parenchymal cells, and in isolated rat liver membrane fractions. The specific binding had KD values ranging from 8 to 10 micrograms/ml. At 37 degrees C beta-VLDL was internalized and degraded in parenchymal cells in culture, but only negligible degradation was measured in suspended cells. In cultured cells the degradation was inhibited by lysosomal and microtubular inhibitors, these agents had no effects in suspended cells. Studies of release suggested internalization in suspended cells and subcellular fractionation experiments confirmed that internalized 125ITC-beta-VLDL reached the lysosomal compartment in cultured cells, but not in suspended cells. Since lactosylated (lac-) beta-VLDL was taken up and degraded efficiently by suspended cells, these cells are not in general unable to transport large lipoprotein particles to the lysosomes. We believe that beta-VLDL does not dissociate from the receptor in the endosomes and therefore is retroendocytosed to the plasma membrane. In isolated parenchymal cells the beta-VLDL binding site is supposedly different from the methylamine-activated-alpha 2-macroglobulin (ma-alpha 2M) binding site, since; 1) Excess beta-VLDL did not reduce ma-alpha 2M binding; 2) In suspended parenchymal cells ma-alpha 2M was readily degraded, whereas beta-VLDL was not degraded and 3) The binding of beta-VLDL was not Ca+(+)-dependent.(ABSTRACT TRUNCATED AT 250 WORDS)

Immunoradiometric assay for serum thyroglobulin: semiquantitative measurement of thyroglobulin in antithyroglobulin-positive sera.

All RIAs for human serum thyroglobulin (Tg) described hitherto are based on the same principle; namely, competitive binding between cold and labeled antigen, followed by separation of bound from free antigen by precipitation of the former by a second antibody. These RIAs for Tg are accurate only when applied to sera free of detectable anti-Tg because the presence of the latter can result in either falsely elevated or falsely depressed values. This report describes a solid phase, sandwich-type, immunoradiometric assay (IRA) for serum Tg. Tg in the sample or standard is first bound to plastic cups coated with rabbit anti-Tg and then measured by the binding of rabbit [125I]anti-Tg. The sensitivity of this assay (detection limit, 2.5 ng Tg/ml serum) and its reproducibility, as indicated by intraassay coefficients of variation(CV20 ng, 11.3%; CV115 ng, 4.1%; CV310 ng, 7.0%) and interassay coefficeients of variation (CV20 ng, 14.0%; CV115 ng, 7.2%; CV310 ng, 7.1%)are comparable to or better than those previousl...