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    BioPatel is offline Member
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    Phosphoenolpyruvate carboxykinase Pyruvate dehydrogenase

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    A histological section of the left ventricle of a deceased 28-year-old white male shows classic contraction band necrosis of the myocardium. Biological specimens confirm the presence of cocaine and metabolites. Activity of which of the following enzymes was most likely increased in the patient's myocardial cells shortly prior to his death?

    A. Phosphoenolpyruvate carboxykinase
    B. Phosphofructokinase-1
    C. Pyruvate dehydrogenase
    D. Succinate dehydrogenase
    E. Transketolase

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    Asclepius1 is offline Ultimate Member 537 points
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    I think he had ischemia before he died so my guess is C. Pyruvate dehydrogenase

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    BioPatel is offline Member
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    Re: Phosphoenolpyruvate carboxykinase Pyruvate dehydrogenase

    Quote Originally Posted by BioPatel
    A histological section of the left ventricle of a deceased 28-year-old white male shows classic contraction band necrosis of the myocardium. Biological specimens confirm the presence of cocaine and metabolites. Activity of which of the following enzymes was most likely increased in the patient's myocardial cells shortly prior to his death?

    A. Phosphoenolpyruvate carboxykinase
    B. Phosphofructokinase-1
    C. Pyruvate dehydrogenase
    D. Succinate dehydrogenase
    E. Transketolase
    The correct answer is B. Cocaine causes contraction band necrosis by blocking the reuptake of norepinephrine, resulting in excessive vasoconstriction of coronary vessels, leading to ischemia and infarction of heart tissue. Under these pathological conditions, myocardial cells switch to anaerobic metabolism and therefore glycolysis becomes the sole source of ATP via substrate-level phosphorylations by phosphoglycerate kinase and pyruvate kinase. Phosphofructokinase-1 (PFK-1) is the rate-limiting enzyme of glycolysis, and its activity would therefore be increased.
    Phosphoenolpyruvate carboxykinase (choice A) is a regulatory enzyme in gluconeogenesis, which is induced by cortisol, epinephrine, and glucagon. It functions in the hepatic synthesis of glucose when energy levels from beta-oxidation of fatty acids are adequate.

    Pyruvate dehydrogenase (choice C) produces acetyl-CoA from pyruvate and coenzyme A, bridging glycolysis and the Krebs cycle. It requires 5 cofactors, including NAD and FAD, which would no longer be produced by the electron transport under hypoxic conditions, decreasing its activity.

    Succinate dehydrogenase (choice D) is a key enzyme of the Krebs cycle, producing a reduced equivalent of FAD to feed into the electron transport chain. It is also known as Complex II. The Krebs cycle only functions if oxygen is in appropriate concentrations since it is regulated by the levels of NADH, which is only consumed by the electron transport chain if there is enough oxygen. The absence of oxygen leads to an accumulation of NADH and a subsequent decrease in the enzyme activities of the Krebs cycle.

    Transketolase (choice E) is a thiamine requiring enzyme of the non-oxidative half of the hexose monophosphate shunt. The shuffling of sugars in the second half of this pathway results in the reentry of glyceraldehyde-3-phosphate and fructose-6-phosphate into the glycolytic pathway. Transketolase activity in red blood cells is used as a clinical marker of thiamine deficiency, markedly decreasing in disorders such as Wernicke-Korsakoff syndrome.

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