A patient presents in your surgery with an inability to maintain blood sugar levels in long

periods (~20 hours) between meals. Tests show that glucose is converted to lactate normally

in liver in the well-fed state, and that pyruvate carboxylase and phosphoenolpyruvate

carboxykinase have normal activities in liver in periods between meals. Your colleague

reminds you that glucagon stimulates glycogen degradation, so you administer glucagon to

the patient (who was well fed prior to the test) and find that blood sugar rises in response as

normal. What pathway is defective in this patient, and what enzyme do you suspect has a

reduced activity? Explain your reasoning.