Question

In: Biology

All of the following enzymes catalyze a committed step except: A. HMG-CoA reductase B. Acetyl-CoA carboxylase...

  1. All of the following enzymes catalyze a committed step except:
    A. HMG-CoA reductase
    B. Acetyl-CoA carboxylase
    C. Fattyacyl-CoA synthetase

    D. Pyruvate dehydrogenase complex
    E. All of the above enzymes catalyze a committed step

Solutions

Expert Solution

Answer: A. HMG-CoA reductase is an enzyme that catalyzes a rate limiting/committed step in mevalonate pathway. This enzyme catalyzes the conversion of HMG-CoA to mevalonic acid. Hence, the enzyme in option A catalyze committed step and is an incorrect answer

B. Acetyl-CoA carboxylase is an enzyme that catalyzes conversion of acetyl-CoA to malonyl-CoA, a rate limiting step in fatty acid biosynthesis. Hence, the enzyme in option B catalyze committed step and is an incorrect answer

C. Fatty acyl-CoA synthetase is an enzyme that is involved in the activation of fatty acid by forming a thioester bond between fatty acid and coenzyme A using ATP. This enzyme is an ligase and activates the fatty acid for oxidation. It is not a committed step in fatty acid oxidation and is the correct answer.

D. Pyruvate dehydrogenase complex consists of three enzyme pyruvate dehydrogenase (E1), dihydrolipoyl transacetylase (E2), and dihydrolipoyl dehydrogenase (E3). This complex converts pyruvate to acetyl-CoA. The step catalyzed by the enzyme pyruvate dehydrogenase (E1) of pyruvate dehydrogenase complex is a rate limiting step. Hence, the enzyme complex in option D catalyze committed step and is incorrect answer


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