Question

Insulin signaling activates the kinase PKB that after a few steps will lead to activation of the enzyme glycogen synthase. This leads to glycogen synthesis. What does PKB do to activate glycogen synthase?

Answer 1

The kinase PKB, activated by insulin signaling, leads to the activation of glycogen synthase by initiating a cascade that results in dephosphorylation of the enzyme, allowing glycogen synthesis. Oppositely, during adrenaline-induced 'fight or flight' response, cAMP and PKA promote glycogen breakdown. Insulin also increases glucose uptake by enhancing glucose transporter presence on the cell membrane.

Step-by-step explanation:

The activation of glycogen synthase, which is necessary for glycogen synthesis, involves the insulin signaling pathway. Specifically, the kinase PKB (also known as Akt) plays a critical role in this process. When insulin binds to its receptor, a series of phosphorylation events are triggered that result in the activation of PKB. PKB then promotes the activation of glycogen synthase by initiating a cascade that ultimately leads to the dephosphorylation or activation of glycogen synthase. This is opposite to the activation of glycogen phosphorylase, which breaks down glycogen into glucose, and is regulated by adrenaline through the cAMP pathway activating protein kinase A (PKA), which promotes glycogen breakdown by phosphorylating glycogen phosphorylase.

Moreover, insulin receptors facilitate the uptake of glucose by increasing the number of high-affinity glucose transporters on the cell membrane. The glucose can then be utilized for energy or converted into glycogen via the action of the now active glycogen synthase enzyme. The phosphorylation state of glycogen synthase is a key regulatory mechanism, whereby insulin signaling leads to a dephosphorylated (and active) state, promoting glycogen synthesis.