Question

the activity of a kinase called src is regulated by phosphorylation. the kinase is inactivated by phosphorylation at a c - terminal tyrosine residue (tyr527) and is activated by interaction with an activated rtk, which stimulates src to autophosphorylate a different tyrosine residue (tyr416). full activation of src requires removal of the inhibitory phosphate group and binding to an activated rtk.
based on this information, which statement about the activity of src kinase is correct?
choose one:
the kinase is active only when tyr416 is dephosphorylated.
the kinase is active only when tyr416 is phosphorylated.
the kinase is active only when tyr527 is phosphorylated and tyr416 is dephosphorylated.
the kinase is active only when tyr527 is dephosphorylated and tyr416 is phosphorylated.
the kinase is active only when tyr527 is phosphorylated.
the kinase is active only when tyr527 is dephosphorylated.

Explanation:

• The problem states that Src kinase is inactivated by phosphorylation at Tyr527. So, for the kinase to be active, Tyr527 must be dephosphorylated.
• It is also stated that the kinase is activated by autophosphorylation at Tyr416. So, Tyr416 must be phosphorylated for the kinase to be active.

Answer:

The kinase is active only when Tyr527 is dephosphorylated and Tyr416 is phosphorylated.