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Title: Protein catabolism in cultured rat yolk sac
Author: Ibbotson, Graham E.
Awarding Body: Keele University
Current Institution: Keele University
Date of Award: 1978
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An in vitro culture technique for the quantitation of pinocytosis in the rat visceral yolk sac was modified, by removing calf serum from the incubation medium, to permit determination of the rate of uptake of substrates in the absence of competing serum proteins. Study of the Endocytic Index of ¹²⁵I-labelled PVP in the absence of calf serum indicated that the substrate provided a suitable marker for determination of the rate of fluid ingestion in serum-free medium. From measurements of the rates of ingestion of [U¹⁴C] sucrose, ¹²⁵I-labelled dBSA and colloidal [¹⁹⁸Au] gold in the presence and absence of calf serum, it was concluded that the first substrate is ingested essentially in the fluid phase, while the other two are ingested mainly adsorbed to the plasma membrane. A detailed study of the uptake of ¹²⁵I-labelled dBSA in the presence of a non-radioactive analogue permitted a kinetic analysis of the affinity of this substrate for binding sites on the plasma membrane. The rate of ingestion of homologous ¹²⁵I-labelled IgG indicated that it is ingested mainly in the adsorbed phase but at a slower rate than ¹²⁵I-labelled dBSA. On re-incubation of yolk sacs 'loaded' in vitro with ¹²⁵I-labelled IgG a significant percentage of the released radioactivity was macromolecular and tentatively identified as ¹²⁵I-labelled IgG. This finding contrasted sharply with that for either ¹²⁵I-labelled PVP, with which little radioactivity was released, or ¹²⁵I-labelled dBSA, with which virtually all the radioactivity released was in a low molecular weight form. The observation that IgG can escape from the tissue intact is compatible with the suggestion that the rat yolk sac is instrumental in the transmission of passive immunity from mother to fetus prior to birth. A number of investigations were performed in an attempt to distinguish the mechanism of release. The findings suggest that release occurred by way of a separate transport vesicle as proposed by A.E. Wild.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QH301 Biology