Question

Which statement about control of glycogen metabolism is INCORRECT? Which statement about control of glycogen metabolism is INCORRECT? Glycogen phosphorylase is activated by phosphorylation. Glucagon signals glycogen breakdown in liver. Epinephrine signals glycogen breakdown in muscle. Glycogen synthase is phosphorylated at only one site.

Answer 1

Answer:

Glycogen synthase is phosphorylated at only one site.

Explanation:

Glycogen synthase has multiple sites where phosphorylation can occur. Glycogen synthase may have 9 or more sites where it can be phosphorylated as a result of which it's activity is down regulated. It simply means that the regulation of this enzyme does not occur through binary on/off switching, in fact it's activity is modulated over a wide range in response to various signals.

In contrast to glycogen phosphorylase which gets activated when it is phosphorylated at it's serine residues, glycogen synthase gets inactivated by phosphorylation.

As soon as another enzyme GSK3β phosphorylates glycogen synthase, it gets inactivated as a result of which glycogen synthesis halts in the liver.