Many metabolic disorders have similar symptoms because of the connections betwee

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.

Explanation / Answer

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.

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