Johnson B C
Oklahoma Medical Research Foundation, Oklahoma City 73104.
J Chromatogr. 1988 May 25;440:499-508. doi: 10.1016/s0021-9673(00)94555-2.
The vitamin K's are 2-methyl-1,4-naphthoquinones. The vitamin is required for the post-translational gamma-carboxylation of glutamyl residues in precursor polypeptides. The vitamin K step in this carboxylation, however, requires not the quinone but the hydroquinone plus oxygen. Thus, the vitamin K-dependent step is a "mixed function" oxidation requiring a reducing compound plus molecular oxygen to provide a form of oxidant (e.g., a free radical, a hydroperoxide) capable of abstracting a particular, slightly labile hydrogen from a glutamyl residue, leaving this position free to accept a carbon dioxide molecule. This oxidation appears similar to that of other mixed function oxidants such as cytochrome P450 plus oxygen, ascorbic acid (with traces of ferrous iron) plus oxygen, ferrous iron plus oxygen, and a number of other systems which function in a wide variety of oxidation. Inhibition by spin-trapping agents suggests a free radical step in the vitamin K hydroquinone-dependent reaction, similar to other mixed function oxidations.
维生素K是2-甲基-1,4-萘醌。该维生素是前体多肽中谷氨酰残基翻译后γ-羧化所必需的。然而，此羧化过程中的维生素K步骤所需的不是醌，而是对苯二酚加氧气。因此，维生素K依赖性步骤是一种“混合功能”氧化反应，需要一种还原化合物加分子氧来提供一种能够从谷氨酰残基夺取一个特定的、略微不稳定的氢的氧化剂形式（例如，自由基、氢过氧化物），使该位置能够接受一个二氧化碳分子。这种氧化反应似乎类似于其他混合功能氧化剂的氧化反应，如细胞色素P450加氧气、抗坏血酸（含微量亚铁离子）加氧气、亚铁离子加氧气，以及许多在各种氧化反应中起作用的其他系统。自旋捕获剂的抑制作用表明，在维生素K对苯二酚依赖性反应中存在自由基步骤，这与其他混合功能氧化反应类似。
