Question
A 1-week-old male newborn is brought to the physician for a follow-up examination after the results of newborn screening showed an increased serum concentration of phenylalanine. Genetic analysis confirms a diagnosis of phenylketonuria. The physician counsels the patient’s family on the recommended dietary restrictions, including avoidance of artificial sweeteners that contain aspartame. Aspartame is a molecule composed of aspartate and phenylalanine and its digestion can lead to hyperphenylalaninemia in patients with phenylketonuria. Which of the following enzymes is primarily responsible for the breakdown of aspartame?
| A. |
Pepsin
|
| B. |
Dipeptidase
|
| C. |
Trypsin
|
| D. |
Chymotrypsin
|
Show Answer
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Correct Answer � B
Explanation
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Answer B) Dipeptidase
Aspartame is primarily cleaved by a brush border enzyme on the villi of the intestinal mucosa.
Dipeptidase
Pepsin
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Pepsin, a gastric endopeptidase, cleaves peptide bonds within protein molecules and targets specific peptide bonds between hydrophobic and aromatic amino acids (e.g., phenylalanine-tryptophan).
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Pepsin does not target peptide bonds involving hydrophilic amino acids such as aspartate. Moreover, aspartame has two terminal amino acids and can only be broken down by an enzyme with exopeptidase activity.
Chymotrypsin
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Chymotrypsin, a pancreatic endopeptidase, cleaves peptide bonds within protein molecules and targets specific peptide bonds between hydrophobic and aromatic amino acids (e.g., phenylalanine-tryptophan).
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Chymotrypsin does not target peptide bonds involving hydrophilic amino acids such as aspartate. Moreover, aspartame has two terminal amino acids and can only be broken down by an enzyme with exopeptidase activity.
Trypsin
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Trypsin, a pancreatic endopeptidase, cleaves peptide bonds within protein molecules and targets specific peptide bonds that contain the positively charged amino acids arginine or lysine.
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Trypsin does not target peptide bonds involving the hydrophobic amino acid phenylalanine or the negatively charged aspartate.
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Moreover, aspartame has two terminal amino acids and can only be broken down by an enzyme with exopeptidase activity.
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