The mannose 6-phosphate receptor is located predominantly in endosomes and the TGN, but about 10% of the mannose 6-phosphate receptor molecules are in the plasma membrane. Suppose you have an antibody that associates with the mannose 6-phosphate receptor and blocks the ability of the receptor to bind mannose 6-phosphate. Suppose further that this association is rapid and effectively irreversible. If you incubate cells with the antibody for a brief time and then wash away excess antibody, the cells continue to sort lysosomal enzymes normally. But if you incubate cells continuously with the antibody for a prolonged time, the cells begin to secrete lysosomal enzymes. a) How would you interpret this result? b) Suppose that the antibody has been fluorescently labeled by covalently attaching a fluorophore. If you examine cells that have been incubated continuously with this labeled antibody, what types of fluorescence patterns would you expect to see at different time points after antibody addition?
2. The mannose 6-phosphate receptor is located predominantly in endosomes and the TGN, but about 10% of the mannose 6-phosphate receptor molecules are in the plasma membrane.
Suppose you have an antibody that associates with the mannose 6-phosphate receptor and blocks the ability of the receptor to bind mannose 6-phosphate. Suppose further that this association is rapid and effectively irreversible.
If you incubate cells with the antibody for a brief time and then wash away excess antibody, the cells continue to sort lysosomal enzymes normally. But if you incubate cells continuously with the antibody for a prolonged time, the cells begin to secrete lysosomal enzymes.
a) How would you interpret this result?
b) Suppose that the antibody has been fluorescently labeled by covalently attaching a fluorophore. If you examine cells that have been incubated continuously with this labeled antibody, what types of fluorescence patterns would you expect to see at different time points after antibody addition?
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