Final answer:
Phosphorylase kinase activates glycogen phosphorylase via phosphorylation, a key event in glycogenolysis to provide glucose during the fight-or-flight response.
Step-by-step explanation:
The enzyme responsible for the activation of glycogen phosphorylase through phosphorylation is phosphorylase kinase (GPK). This activation occurs during the process of glycogenolysis, where glycogen is broken down into glucose monomers. Hormones such as adrenaline (epinephrine) and glucagon can trigger this process by binding to receptors that initiate a cascade of events leading to the formation of cyclic AMP (cAMP).
cAMP then activates protein kinase A (PKA), which subsequently phosphorylates phosphorylase kinase, turning it into its active form. Active GPK then phosphorylates the inactive form of glycogen phosphorylase (b form), converting it into the active form (a form). This active enzyme catalyzes the hydrolysis of glycogen, releasing glucose-1-phosphate, which can be converted into glucose-6-phosphate and utilized for energy during the fight-or-flight response.
In summary, phosphorylase kinase plays a critical role in the rapid production of glucose from glycogen stores within the liver, providing energy when the body faces immediate demands.