Activation of insulin receptors by binding of insulin results in numerous changes in the activity of other signaling proteins. Some of these changes are increases in activity, some are decreases. Of the following enzymes, which one has an increased level of activity after insulin binds its receptor?
A) GSK3
B) glycogen synthase
C) glycogen phosphorylase
D) PKA
E) protein phosphatase inhibitor 1 (PPI-1)

Question

Quizplus · Accepted Answer

Insulin binding to its receptor activates a signaling cascade that leads to the activation of glycogen synthase, promoting glycogen synthesis.  One of the effects of insulin is the activation of phosphodiesterase (PDE) which leads to decreases in cAMP levels. Decreased cAMP results in decreased PKA activity and, as a consequence, diminished phosphorylation of its substrates. PKA normally phosphorylates and activates PPI-1 which then inhibits protein phosphatase-1 (PP-1) activity. Diminished PKA and elevated protein phosphatase activity in response to insulin combine to convert glycogen phosphorylase to its inactive form and glycogen synthase to its active form, with the result that not only is glucose funneled to glycolytic products, but glycogen content is increased as well.

Activation of Insulin Receptors by Binding of Insulin Results in Numerous