Endocytosis and subsequent processing of 125I-labelled immunoglobulin G by guinea pig yolk sac in vitro.
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 degrees C and to paraformaldehyde-treated tissue at 37 degrees C was time- and temperature-dependent and showed saturation kinetics (Kd,4 degrees C = 2.9 X 10(-6) M, Kd,37 degrees C = 5.3 X 10(-6) M). Uptake was studied at 37 degrees 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 degrees 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.
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D000963:Antimetabolites / Q000494:pharmacology; D004705:Endocytosis / Q000187:drug effects; D005260:Female; D005557:Formaldehyde / Q000494:pharmacology; D006168:Guinea Pigs; D007074:Immunoglobulin G / Q000378:metabolism*; D066298:In Vitro Techniques; D007457:Iodine Radioisotopes; D011108:Polymers / Q000494:pharmacology; D011480:Protease Inhibitors / Q000494:pharmacology; D011485:Protein Binding; D012710:Serum Albumin, Bovine / Q000378:metabolism; D013395:Sucrose / Q000378:metabolism; D015017:Yolk Sac / Q000378:metabolism*
D000963:Antimetabolites; D007074:Immunoglobulin G; D007457:Iodine Radioisotopes; D011108:Polymers; D011480:Protease Inhibitors; D005557:Formaldehyde; D012710:Serum Albumin, Bovine; D013395:Sucrose; D000255:Adenosine Triphosphate; C003043:paraform