支链氨基酸分解代谢
中文名称
通路描述
支链氨基酸（亮氨酸、异亮氨酸和缬氨酸）都是必需氨基酸（即饮食中必需摄入的氨基酸）。它们是肌肉蛋白的主要成分。这些氨基酸的分解代谢始于由作用于所有三种氨基酸的酶催化的两个共同步骤：可逆的支链氨基酸转氨基作用，以及由支链酮酸脱氢酶复合体催化的不可逆氧化脱羧作用。异亮酰-CoA 由亮氨酸通过这两个反应产生，α-甲基丁酰-CoA 由异亮氨酸产生，异丁酰-CoA 由缬氨酸产生。这些酰基-CoA 发生脱氢反应，由三种不同但相关的酶催化，然后分解途径分叉。亮氨酸最终转化为乙酰-CoA 和乙酰乙酸；异亮氨酸转化为乙酰-CoA 和琥珀酰-CoA；缬氨酸转化为琥珀酰-CoA。在饥饿条件下，蛋白质分解产生所有三种氨基酸的大量物质。在肌肉中，亮氨酸、异亮氨酸和缬氨酸分解的最终产物可通过三羧酸循环完全氧化；在肝脏中，它们可定向合成酮体（乙酰乙酸和乙酰-CoA）和葡萄糖（琥珀酰-CoA）（Neinast 等，2019）。
英文描述
Branched-chain amino acid catabolism The branched-chain amino acids, leucine, isoleucine, and valine, are all essential amino acids (i.e., ones required in the diet). They are major constituents of muscle protein. The breakdown of these amino acids starts with two common steps catalyzed by enzymes that act on all three amino acids: reversible transamination by branched-chain amino acid aminotransferase, and irreversible oxidative decarboxylation by the branched-chain ketoacid dehydrogenase complex. Isovaleryl-CoA is produced from leucine by these two reactions, alpha-methylbutyryl-CoA from isoleucine, and isobutyryl-CoA from valine. These acyl-CoA's undergo dehydrogenation, catalyzed by three different but related enzymes, and the breakdown pathways then diverge. Leucine is ultimately converted to acetyl-CoA and acetoacetate; isoleucine to acetyl-CoA and succinyl-CoA; and valine to succinyl-CoA. Under fasting conditions, substantial amounts of all three amino acids are generated by protein breakdown. In muscle, the final products of leucine, isoleucine, and valine catabolism can be fully oxidized via the citric acid cycle; in liver they can be directed toward the synthesis of ketone bodies (acetoacetate and acetyl-CoA) and glucose (succinyl-CoA) (Neinast et al. 2019).
所含基因
21 个基因