Question

Loss of activity for which enzyme do you believe is the cause of the problem in this child. Briefly explain and also say why it could not have been one of the other enzymes.

b) a 2 month old boy is brought to the emergency room in a coma after sleeping through the night and failing to awaken in the morning. He is given intravenous glucose and awakens. Serum levels of pyruvate, lactate and alanine are elevated. A muscle biopsy shows no abnormalities and vitamin supplementation is ineffective. Which of the following is the most likely diagnosis?

a. PEP carboxykinase

b. glycogen phosphorylase which is a glycogen catabolic enzyme

c. aldolase which catalyzes formation of ga-3-p and DHAP from f1,6bp?

Answer 1

Correct option is a) PEP carboxykinase. This is an enzyme of gluconeogenesis (synthesis of glucose from non-carbohydrate sources) where it converts oxaloacetate into phosphoenol pyruvate at the cost of GTP molecule. Oxalate formed from the pyruvate by enzyme pyruvate carboxylase. Phosphoenol pyruvate now forms glucose by the enzymes of gluconeogenic pathway. Alanine, lactic acid and pyruvate are precursors for gluconeogenesis, in the absence of phosphoenolpyruvate carboxykinase (PEP carboxykinase) these precursors accumulate in blood. Due to loss of this enzyme child faces hypoglycemia (low concentration of glucose in blood).

Glycogen phosphorylase and aldolase are not responsible for abovementioned disorder of child because

(1) Glycogen phosphorylase catalyze the glycogenolysis in which glycogen is breakdown to glucose-1-phosphate and it maintains the blood glucose level.

(2) Aldolase is an enzyme of glycolysis pathway where it catalyze the formation of glyceraldehyde-3-phosphate (GA-3-P) and dihydroxyacetone phosphate (DHAP) from fructose-1,6-bisphosphate and leads to pyruvate formation.