Understanding the Role of Glucagon in Regulating Blood Glucose Levels and Energy Metabolism

A hormone secreted by the pancreatic alpha cells that increases blood glucose concentrationSecreted when blood glucose levels are lowLeads to increase in [cAMP]Indirectly leads to phosphorylation of bifunctional enzyme – activates F26BPase

The hormone that meets the given description is glucagon

The hormone that meets the given description is glucagon. Glucagon is a hormone secreted by the alpha cells in the pancreas when blood glucose levels are low. Its primary function is to increase blood glucose concentration to ensure adequate energy supply for the body.

When glucagon is released into the bloodstream, it binds to specific receptors on target cells, mainly liver cells. This binding activates a signaling pathway that involves the generation of the second messenger cyclic adenosine monophosphate (cAMP).

The increase in cAMP levels inside the target cells triggers a series of intracellular events. One of the significant effects of increased cAMP is the activation of protein kinase A (PKA), an enzyme that adds phosphate groups to target proteins. This phosphorylation process alters the function of target proteins and activates or deactivates them.

With regards to the mentioned bifunctional enzyme, glucagon indirectly leads to the phosphorylation and activation of fructose-2,6-bisphosphatase (F26BPase). F26BPase is an enzyme involved in the regulation of glucose metabolism. Phosphorylation of F26BPase by PKA decreases its activity, leading to a decrease in the levels of another molecule called fructose-2,6-bisphosphate (F26BP).

A decrease in F26BP levels inhibits the activity of another enzyme called phosphofructokinase-2 (PFK-2), which is responsible for producing fructose-2,6-bisphosphate. Inhibition of PFK-2 subsequently decreases the production of fructose-2,6-bisphosphate, resulting in a decrease in its downstream product, fructose-1,6-bisphosphate (F16BP).

The decreased levels of F16BP inhibit a key step in glycolysis, slowing down the breakdown of glucose for energy production. This brake on glycolysis allows the liver to redirect glucose towards other metabolic pathways, such as gluconeogenesis (the production of glucose from non-carbohydrate sources). As a result, the blood glucose concentration increases, helping to restore glucose homeostasis.

In summary, when blood glucose levels are low, glucagon is secreted by pancreatic alpha cells. Glucagon increases cAMP levels and activates PKA. PKA phosphorylates and activates various target proteins, including F26BPase. Activated F26BPase decreases the levels of F26BP, inhibiting PFK-2 and slowing down glycolysis. This leads to an increase in blood glucose concentration through enhanced gluconeogenesis.

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