Mouse oocytes and preimplantation embryos bear the two sub-units of interferon-gamma receptor

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Mathematical model for the determination of metabolite fluxes in Saccharomyces cerevisiae

We present a mathematical model to determine the absolute values of flux leading to the formation and the disappearance of ethanol and acetyl-CoA in Saccharomyces cerevisiae under repressed state conditions. Cells were fed with [1-13Clglucose with or without unlabeled ethanol. Addition of unlabeled ethanol induces a modulation, with time, of the fractional enrichment of this compound. This experimental approach allows us to obtain the relationships between metabolite fluxes and the other parameters (fractional enrichment, concentration and time). Metabolites are analysed by 1H-, 13C-NMR and enzymatic methods. The validity of the present model is supported by the data obtained from similar experiments using unlabeled ethanol as a sole carbon source and non-NMR techniques

Binding and cross-linking of recombinant mouse interferon-gamma to receptors in mouse leukemic L1210 cells; interferon-gamma internalization and receptor down-regulation

Recombinant E. coli-derived murine IFN-gamma (Mu-rIFN-gamma; 5 X 10(7) U/mg) was radiolabeled with 125I by the chloramine-T method without loss of its antiviral activity. The 125I-Mu-rIFN-gamma showed specific binding to L1210 cells. Scatchard analysis indicates about 4000 binding sites per cell and an apparent Kd of 5 X 10(-10)M. Binding of 125I-Mu-rIFN-gamma to cells was inhibited by both natural (glycosylated) and rIFN-gamma, but not by IFN-alpha/beta. Receptor-bound 125I-Mu-rIFN-gamma was rapidly internalized when incubation temperature was raised from 4 degrees C to 37 degrees C. On internalization, almost no IFN-gamma degradation was observed during 16 hr incubation. 125I-Mu-rIFN-gamma binding capacity decreased in cells preincubated with low doses of unlabeled Mu-rIFN-gamma, but not with IFN-alpha/beta. This receptor down-regulation was dose-dependent: 90% reduction of 125I-Mu-rIFN-gamma binding was observed after preincubation with 100 U/ml. After removal of IFN-gamma from the culture medium, the binding capacity increased with time. However, reappearance of receptor was completely blocked by cycloheximide or tunicamycin, suggesting that re-expression of receptors is not due to recycling but to the synthesis of new receptors, and that the receptor is probably a glycoprotein. Cross-linking of 125I-Mu-rIFN-gamma to surface L1210 cell proteins by using bifunctional agents yielded a predominant complex of m.w. 110,000 +/- 5000. Thus, assuming a bimolecular complex, the m.w. of the receptor or receptor subunit would be close to 95,000 +/- 5000. The formation of such a complex appeared highly specific on the basis of the following criteria: it could be inhibited by the addition of Mu-rIFN-gamma but not by Mu-rIFN-alpha/beta, it was not obtained in cells pretreated with IFN-gamma to induce down-regulation of IFN-gamma receptors, and it was also identified in the IFN-alpha/beta-resistant L1210R cell line, known to be sensitive to IFN-gamma and which we have recently shown to express IFN-gamma receptors