Updated: 8/10/2019

Propionic Acid Pathway

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Overview
  •  Production
    • β-oxidation of odd-numbered fatty acids
      • 2 carbon acetyl-CoA groups removed from chain until there are 5 carbons remaining
      • 5 carbon chain split into 1 acetyl-CoA (2C) + 1 propionyl-CoA (3C)
  • Pathway 
    • propionyl-CoA → methylmalonyl-CoA
      • catalyzed by propionyl-CoA carboxylase
        • requires biotin (B7)
    • methylmalonyl-CoA → succinyl-CoA
      • catalyzed by methylmalonyl-CoA mutase
        • requires B12
      • deficiency of B12 results in a blockage of this step
        • result is ↑↑↑ methylmalonate
        • can cause irreversible neuropathy
          • due to pathologic synthesis of myelin with methylmalonate
        • a means to determine whether a patient with megaloblastic anemia is deficient in folate or B12
          • methylmalonic aciduria not see in folate deficiencies
    • succinyl-CoA → citric acid cycle
      • can be converted to malate
        • is gluconeogenic
          • exception to rule that fatty acids can be converted to glucose
 

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Questions (2)
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(M1.BC.15.72) A 3-day-old female infant presents with poor feeding, lethargy, vomiting after feeding, and seizures. Labs revealed ketoacidosis and elevated hydroxypropionic acid levels. Upon administration of parenteral glucose and protein devoid of valine, leucine, methionine, and threonine, and carnitine, the infant began to recover. Which of the following enzymes is most likely deficient in this infant? Tested Concept

QID: 106505
1

Branched-chain ketoacid dehydrogenase

39%

(94/239)

2

Phenylalanine hydroxylase

8%

(18/239)

3

Propionyl-CoA carboxylase

43%

(102/239)

4

Cystathionine synthase

4%

(10/239)

5

Homogentisate oxidase

4%

(10/239)

M 2 D

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