Case Study Glycogen

1. Would you expect glycogen to accumulate in the muscle of this patient? Why or why not? (5 points)

Yes, I would expect glycogen to accumulate in the muscle of this patient. The patient has type V glycogen storage disease which means he/she does not have muscle glycogen phosphorylase. Phosphorylase is an enzyme involved in the catalase breakdown of glycogen to glucose for use in muscle. This process is called glycogenolysis which is the breakdown of glycogen into individual glucose units in the form of glucose 1-phosphate. With-out that process glycogen will build up in the muscle because it is not getting broken down to glucose 1-phosphate that can be used for energy.

2. Would you expect lactate to accumulate in the muscle or blood of this patient during exercise? Why or why not? (5 points)

No, I would not expect lactate to accumulate in the muscle or blood of this patient during exercise.

Lactate is made from the anaerobic metabolism of glucose which travels to the liver and is converted back to glucose via gluconeogenesis; that cycle is the Cori cycle. Since the patient cannot break down glycogen to glucose, the Cori cycle could not be completed because there will not be any glucose 6-phosphate made into lactate by a pyruvate.

3. What fuels would you expect this patient to use during exercise? (10 points)

Since the patient cannot use glycose as a form of energy for the muscle I would expect this patient to use fuels such as fatty acids and proteins.

1. In normal individuals, the capacity of the liver to phosphorylate fructose (fructokinase activity) greatly exceeds the liver's capacity to split fructose 1-phosphate (aldolase B activity). Why is a deficiency of fructokinase a less serious genetic defect than a deficiency of fructose 1-phosphate aldolase? Consider what happens to fructose in each case and what effect this has on hepatic metabolism. (20

points)

The deficiency of fructokinase is not as serious as deficiency of fructose 1-phospate aldolase because fructokinase is the first enzyme involved in the degradation of fructose to fructose-1-phosphate in the liver, with the deficiency this cannot be done so fructose is either excreted in the urine or metabolized to fructose-6-phosphate by different processes.
The deficiency of fructose 1-phosphate aldolase is much more serious because fructose-1-phosphate that is created from fructose plays an important part of glucose metabolism. In a person without the deficiency, fructose entering a cell rapidly phosphorylated to fructose 1-phosphate which is a precursor of glucogenolysis and gluconeogenesis. A person with the deficiency will have a build-up of fructose 1-phosphate resulting in a blockage of glycogenolysis and gluconeogenesis and blocks the remaining abnormal hepatic aldolase. With those processes blocked there will be a lack of Pi and ATP. Many symptoms can occur like“vomiting, hypoglycemia, failure to thrive, cachexia, hepatomegaly, jaundice, coagulopathy, coma, renal Fanconi syndrome, and severe metabolic acidosis.”1