Question

Many metabolic disorders have similar symptoms because of the connections between pathways. The more severe form of lactate dehydrogenase deficiency and a deficiency in phosphofructokinase-1 in muscle can have similar symptoms of exercise intolerance, including fatigue and muscle pain during strenuous exercise. Individuals with phosphofructokinase-1 deficiency have more severe symptoms. Treatment for both individuals includes avoidance of high-intensity exercise.

Along with other similar symptoms, both deficiencies can also result in reduced lactate levels during exercise. In order to distinguish between these two disorders, a physician could test the patient's lactate levels during exercise before and after administering glycerol. What would be the expected results if this test were performed?

Choose one or more:

A. Lactate levels would be low after intense exercise and would increase after glycerol was administered if the patient has a deficiency in lactate dehydrogenase.

B. Lactate levels would be low after intense exercise and would not increase after glycerol was administered if the patient has a deficiency in muscle phosphofructokinase-1.

C. Lactate levels would be low after intense exercise and would not increase after glycerol was administered if the patient has a deficiency in lactate dehydrogenase.

D. Lactate levels would be low after intense exercise and would increase after glycerol was administered if the patient has a deficiency in muscle phosphofructokinase-1.

Answer 1

Answer: Options C and D are correct.
Explanation:
Lactate dehydrogenase catalyzes the following reaction.
Pyruvate + NAD+ --------> Lactate + NADH + H+
PFK catalyzes the following reaction.
Fructose 6-phosphate + ATP -----> Fructose 1,6-bisphosphate + ADP

Glycerol is converted to glycerladehyde-3-phosphate/DHAP and enters glycolysis.
If a person is mutant for lactate dehydrogenase, lactate levels would not increase even after the administration of glycerol.
If a person is mutant for PFK, lactate levels would increase after the administration of glycerol as G-3-P is a downstream component of PFK reaction in glycolysis.