A 17-Year-Old Child Was Discovered Unconscious at Home After Being

A 17-year-old child was discovered unconscious at home after being diagnosed with type 1 diabetes mellitus. According to his family, the patient did not feel well last night and skipped supper, but he nevertheless took his customary insulin dosage. His fingerstick blood glucose level is 32 mg/dL, so paramedics promptly give intramuscular glucagon. In hepatocytes, glucagon interacts to a transmembrane receptor, promoting intracellular GTP binding to a particular receptor-associated protein. This results in further downstream signaling and fast metabolic changes inside hepatocytes, such as a rapid depletion in intracellular glycogen reserves and glucose release into the blood. Which of the following is the most likely cause of these effects?

A) cGMP-dependent protein kinase
B) Janus tyrosine kinase
C) Phosphodiesterase
D) Protein kinase A
E) Tyrosine-specific protein kinase