Covalent modification vs. allosteric regulation
In the liver, glucagon signaling leads to phosphorylation of glycogen phosphorylase, which activates it. This is an example of:
Answer C: explanation for every choice
A
Allosteric regulation is reversible, noncovalent binding of an effector at a site other than the active site, such as AMP activating muscle phosphorylase.
B
Zymogen activation is irreversible cleavage of an inactive precursor, such as trypsinogen becoming trypsin.
C
Correct. Phosphorylase kinase covalently attaches a phosphate to a serine residue, and a phosphatase can remove it.
D
Feedback inhibition is a pathway's end product inhibiting an earlier enzyme in the same pathway, usually allosterically.
TakeawayPhosphorylation: covalent and reversible. Zymogen cleavage: covalent and irreversible. Allosteric: noncovalent.
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Reviewed 2026-11-05 by a medical student. Spot an error? Report it with question ID bb7.