Α-氧化

α-氧化的步骤

α-氧化脂肪酸降解的一种方式,不过较β-氧化少见。其中,α-氧化是指在α-碳上的氧化。这种代谢途径发生在某些因β-碳被封闭(如连有甲基)而无法进行β-氧化的脂肪酸中,例如植烷酸;其产物通常可以因此进入β-氧化而按照常例被代谢掉。

不同于β-氧化的是,α-氧化可以发生在游离的脂肪酸上,不需脂肪酸与ATP形成混酐而被活化;而且,这种过程不产生ATP,既可在内质网发生,也可在线粒体过氧化物酶体发生。

途径

下面以植烷酸为例说明α-氧化的过程(这一过程被认为是完全在过氧化物酶体中进行的)。

  1. 植烷酸CoA缩合,产生植烷酰CoA
  2. 植烷酰CoA在植烷酰CoA双加氧酶催化和 Fe2+、O2维生素C存在下,被氧化为2-羟基植烷酰CoA
  3. 2-羟基植烷酰CoA在2-羟基植烷酰CoA裂合酶作用下,发生裂解,产生降植烷醛(少一个碳)和甲酰CoA。这一反应需要TPP。(甲酰CoA继续被降解,可分别产生甲酸根离子和二氧化碳
  4. 降植烷醛在醛脱氢酶催化下被氧化为降植烷酸,而降植烷酸由于β-碳不再封闭(原有甲基已被"移"至α-碳上),因此可以进入β-氧化。

缺乏症

植烷酸和其前体植烷醇大量存在于人的饮食中,因此α-氧化在体内十分重要。然而,有一种Refsum氏病的患者,先天缺乏α-氧化的相关酶(常见为植烷酰CoA双加氧酶),导致植烷酸在体内积累,从而造成神经损伤。

参考文献

引用

来源

  • Casteels, M; Foulon; Mannaerts; Van Veldhoven, Alpha-oxidation of 3-methyl-substituted fatty acids and its thiamine dependence, European journal of biochemistry / FEBS, 2003, 270 (8): 1619–1627, PMID 12694175 
  • Quant, Patti A.; Eaton, Simon (编), Current views of fatty acid oxidation and ketogenesis : from organelles to point mutations 466 2nd, New York, NY: Kluwer Acad./Plenum Publ.: 292–295, 1999, ISBN 0306462001 

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