Which of the following mechanisms is not directly involved in inactivating an activated RTK?

(a) dephosphorylation by serine/threonine phosphatases
(b) dephosphorylation by protein tyrosine phosphatases
(c) removal of the RTK from the plasma membrane by endocytosis
(d) digestion of the RTK in lysosomes


(a) RTKs are phosphorylated on tyrosines by their dimerization partner, which is also a tyrosine kinase, and thus the reversal of these phosphorylations involves protein tyrosine phosphatases, and not protein serine/threonine phosphatases. Endocytosis of the receptor and its ultimate digestion in the lysosome are other methods that the cell uses to down-regulate active receptors.

Biology & Microbiology

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