We have developed conditions for studying the binding, uptake, degradation and transport of 125I-labelled IgG by yolk sac in vitro. Specific binding to tissue at 4°C and to paraformaldehyde-treated tissue at 37°C was time- and temperature-dependent and showed saturated kinetics (K(d,4°C) = 2.9 x 10-6M, K(d,37°C) = 5.3 x 10-6 M). Uptake was studied at 37°C using untreated tissue (K(uptake) = 13.3 x 10-6 M) and was inhibited by preincubation with metabolic poisons but not with cycloheximide. Tissue that had been incubated with 125I-labelled IgG at 37°C released radiolabelled degradation products and intact 125I-labelled IgG into the medium. Experiments with paraformaldehyde-treated and untreated tissue showed that release of intact 125I-labelled IgG was mostly the result of ligand dissociation from surface binding sites. However, more 125I-labelled IgG was released from untreated tissue than could be accounted for solely by loss of surface-bound ligand and the difference was presumed to reflect uptake, transport and exocytosis of 125I-labelled IgG. Degradation of 125I-labelled IgG was inhibited by leupeptin and lysosomotropic amines. These drugs had no detectable effect on 125I-labelled IgG release. The results suggest that degradation and transport of IgG are not intimately related and are consistent with a previously proposed model for IgG transport via coated vesicles which do not fuse with lysosomes and for non-selective uptake into another class of vesicle which does fuse with lysosomes.
|Original language||English (US)|
|Number of pages||12|
|State||Published - 1985|
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