Clarification of the mechanism of menaquinone-4 formation from naphthoquinone ring and isoprenoid side-chain in major tissues of rats

阐明大鼠主要组织中萘醌环和类异戊二烯侧链形成甲基萘醌-4 的机制

基本信息

批准号：
07660150
负责人：
KOMAI Michio
金额：
$ 1.47万
依托单位：
Tohoku University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1995
资助国家：
日本
起止时间：
1995 至 1996
项目状态：
已结题

项目摘要

Phylloquinone (PK=VK_1) and the menaquinones (MK-n, VK_2) are naturally occurring forms of vitamin K.Most of the menaquinone series are synthesized microbiologically, but we have reported elsewhere that menaquinone-4 (MK-4) is an usual in being synthesized by the conversion of ingested phylloquinone or menadione (VK_3) in the major tissues of germ-free rats or mice (which lack an intestinal microflora). The present research was undertaken to clarify the mechanism of MK-4 formation from naphthoquinone ring and isoprenoid side-chain in major tissues of rats.In the first experiment, the distribution of phylloquinone and MK-4 in various tissues were assessed after the oral administration of phylloquinone. Wistar rats were fed a vitamin-K-deficient diet for 9 days, fasted for 24h and then given phylloquinoe orally at 4mg/kg body weight. Rats were sacrificed 0,6,12, and 24h after the administration, and an analysis was made of the vitamin K analogues in the plasma, liver, brain, testis, kidn … More ey, and spleen. The phylloquinone concentration in plasma and the tissues reached a peak 6h after the oral administration of phylloquinone. By contrast, the concentration of MK-4 peaked in the liver, plasma, kidney, and spleen at 12h, and in brain and testis at 24h. This data suggests that the ingested phylloquinone was probably converted into MK-4 within the tissues themselves, rather than via hepatic metabolism. The evidence for this is that, after phylloquinone administration, (i) in each of the tissues, the MK-4 concentration increased much more slowly than that of phylloquinone, and (ii) the MK-4 concentration in the plasma and liver reached only much lower levels than those seen in other tissues.In the second and third experiments in which the labeled phylloquinone was used, it was shown that [side-chain-^3H]-label of phylloquinone was not incorporated into the side-chain of MK-4, however, the radioacitivity originated from the [ring-8]-^<14>C-phylloquinone was detected in the MK-4 fraction of various tissues. These phenomena indicate that the isoprenoid side-chain of phylloquinone once separate from its maphthoquinone ring, then it may be replaced by other isoprenoid side chain such as geranyl-geranyl group within each tissue, and suggest that K_3 must be detected in the midst of the reaction. Actually, the radioactivity from [ring-8]-^<14>C-phylloquinone was clearly detected in the K_3 fraction of heart. In the final experiment, the converted MK-4 fraction was collected and purified, then the identification of estimated MK-4 molecule was undertaken by the high-resolution mass spectrometry, and it was finally identified as MK-4. Less

叶绿醌 (PK=VK_1) 和甲基萘醌 (MK-n, VK_2) 是维生素 K 的天然形式。大多数甲基萘醌系列是通过微生物合成的，但我们在其他地方报道过甲基萘醌-4 (MK-4) 是一种常见的通过摄入的叶绿醌或甲萘醌 (VK_3) 在无菌大鼠或小鼠（缺乏本研究旨在阐明大鼠主要组织中萘醌环和类异戊二烯侧链形成 MK-4 的机制。在第一个实验中，研究了叶绿醌和 MK-4 在各组织中的分布。口服叶绿醌后进行评估，Wistar 大鼠喂食缺乏维生素 K 的饮食 9 天，禁食 24 小时，然后在 20 ℃ 口服叶绿醌。给药后0、6、12和24小时处死大鼠4mg/kg体重，并对血浆、肝脏、脑、睾丸、肾和脾中的维生素K类似物进行分析。口服叶绿醌后6小时，血浆和组织中的浓度达到峰值，而MK-4的浓度在肝脏、血浆、肾脏和组织中达到峰值。 12 小时在脾脏中，以及在 24 小时在大脑和睾丸中，该数据表明摄入的叶绿醌可能在组织本身内转化为 MK-4，而不是通过肝脏代谢。这方面的证据是，在施用叶绿醌后，（i）。 ) 在每个组织中，MK-4 浓度的增加比叶绿醌慢得多，并且 (ii) 血浆和肝脏中的 MK-4 浓度达到仅比在其他组织中看到的水平低得多。在使用标记的叶绿醌的第二和第三个实验中，表明叶绿醌的[侧链-^3H]-标记没有掺入到叶绿醌的侧链中。然而，对于MK-4，在各种组织的MK-4部分中检测到源自[环8]-^ 14 C-叶绿醌的放射性。这些现象表明类异戊二烯。叶绿醌的侧链一旦从其萘醌环上分离，那么它可能被各组织内的其他类异戊二烯侧链如香叶基-香叶基基团取代，这表明K_3必须在反应过程中被检测到。在心脏的K_3级分中清楚地检测到来自[ring-8]-^ 14 C-叶绿醌。在最终实验中，收集并纯化了转化的MK-4级分，然后通过高分辨率质谱对估计的MK-4分子进行鉴定，最终鉴定为MK-4。