monam84
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When exercising, a 19 year old man develops painful cramps that are associated withacute episodes of myoglobinuria. Administration of oral glucose during the acute episode does not alleviate the symptoms. Additional studies show that a hemolytic anemia is present. The patient most likely suffers from a deficiency of which enzyme?
a- branching enzyme
b- muscle phosphorylasee
c- glucose 6 phosphatase
d-liver phosphorylase
e- phosphofructokinase
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| doc179
Forum Guru
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B
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| monam84
Forum Senior
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Its a tricky question, hint: giving glucose does not help.
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| new_n_lost
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e- phosphofructokinase
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| virgola82
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As I read it I suddenly said B but thinking about your hint E should be the right answer: it is only glycolytic enzyme among those listed so because glucose doesn't help it should mean that glycolisis doesn't work. It was tricky... Hope they are not gonna be like this on exam....
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| doc179
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yeah...I considered that , but then did not think much about it. NNL seems right.
go for E
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| jole
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thought it was B can u pls explain why its E.Thanks.
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| monam84
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Answer:
Phosphofructokinase is correct. PFK, the rate limiting enzyme of glyolysis coverts f-6-p to f-1,6-p. Deficiency of PFK mimics the painful cramps seen in patients with McArdle's disease. In McArdles, there is a def of muscle glycogen phosphorylase and inability to generate glucose from glycogen, thus depriving the muscle of an energy source and leading to rhabdomyolysis with concomitant myoglobinuria during exercise. Defiency of PFK does NOT alter glycogenolysis , however the glucose that is produced can not be used for energy; them uscle reacts during exercise in a similar fashion to McArdle's. In general, enzyme deficiency involving glycolysis lead to hemolytic anemias. RBCs rely on anaerobic glycolyis for ATP and therefore hemolyze.
The key to this question is knowing that the patient is not responding to glucose so there must be a defect in the glycolytic pathway. In McArdles the glycolytic pathway works to produce energy so admin of glucose would alleviate symptoms. Similarly, if you give a patient with PFK deficiency glucose, they cant use that for energy so it doesnt help.
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| doc179
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very nice qn. Thanx for the explanation.
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| Luckyall
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 nice Qs
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| jole
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Wow the explanation is soo cool!!thanks alot.
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