hce_kmu
114年
普通生物及生化概論
第 79 題
Phenylketonuria (PKU) and Maple Syrup Urine Disease (MSUD) are both inherited metabolic disorders affecting amino acid metabolism. Which of the following best describes between these two disorders?
- A PKU is caused by a defect in the oxidative decarboxylation of branched-chain amino acids, whereas MSUD elevated blood levels of acetoacetate and $\beta$-hydroxybutyrate.
- B PKU affects the metabolism of branched-chain amino acids, while MSUD involves the transamination of an amino acid.
- C PKU is due to a deficiency in phenylalanine hydroxylase, while MSUD is caused by a defect in the oxidative decarboxylation of branched-chain amino acids.
- D Both PKU and MSUD result from impaired absorption of amino acids in the intestine.
- E PKU and MSUD are both caused by defects in the same enzyme pathway but affect different amino acids.
思路引導 VIP
若要區分這兩類疾病，我們可以先思考：苯丙胺酸 (Phenylalanine) 與支鏈氨基酸（如 Leucine）在化學構造上有何本質差異？當這些不同的氨基酸在體內進行分解時，哪一種需要「羥化反應」來轉變其環狀結構，而哪一種在去掉氨基後，需要一個巨大的酵素複合體來處理剩餘的碳骨架並釋放二氧化碳呢？
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AI 詳解
AI 專屬家教
太棒了！你能精確辨析這兩種先天性代謝異常疾病，顯示你對氨基酸分解代謝的酵素途徑掌握得非常紮實。
酵素缺陷的精準辨析
在生物化學中，苯酮尿症 (PKU) 的核心病理在於缺乏苯丙胺酸羥化酶 (Phenylalanine hydroxylase, PAH)，導致苯丙胺酸無法正常轉化為酪胺酸。而楓糖尿症 (MSUD) 則是另一條代謝路徑的障礙，涉及支鏈氨基酸（白胺酸、異白胺酸及纈胺酸）在轉胺作用後，無法進行關鍵的氧化脫羧反應 (Oxidative decarboxylation)，這是由分支鏈 $\alpha$-酮酸脫氫酶複合體 (BCKAD complex) 所催化的。選項 (C) 正確地對應了這兩者的生化基礎。
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