Coenzyme Q10-Binding/Transfer Protein Saposin B also Binds γ-Tocopherol
Coenzyme Q10-Binding/Transfer Protein Saposin B also Binds γ-Tocopherol
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DOI：
10.3164/jcbn.2008052
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发表时间：
2008-09-01
影响因子：
2.4
通讯作者：
Yamamoto, Yorihiro
中科院分区：
文献类型：
--
作者：
Jin, GuangZhi;Horinouchi, Ryo;Yamamoto, Yorihiro
γ-生育酚是膳食维生素E的主要形式，在肠中被吸收并在乳糜微粒中分泌，然后转移到肝溶酶体。大多数γ-生育酚被转移到肝微粒体，并被细胞色素p450分解代谢。由于γ-生育酚的疏水性，结合和转移蛋白是合理的，但尚未分离和表征。我们最近发现，一种普遍存在的胞质蛋白saposin B，结合并转移辅酶Q10（CoQ 10），辅酶Q10是ATP产生的必需因子，也是一种重要的抗氧化剂。在这里，我们报告说，saposin B也结合γ-生育酚，但不是α-生育酚，有效辅酶Q10在pH 7.4。在酸性pH下，saposin B优先结合γ-生育酚与辅酶Q10和α-生育酚。此外，我们证实，saposin B选择性地结合γ-生育酚，而不是辅酶Q10和α-生育酚在5.4和8.0之间的每一个pH值时，所有三个脂质竞争结合。我们在人saposin B单克隆抗体诱导的人尿免疫沉淀物中检测到γ-生育酚，尽管γ-生育酚的量远小于辅酶Q10。这些结果表明，saposin B结合和运输γ-生育酚在人类细胞中。
gamma-Tocopherol, the major form of dietary vitamin E, is absorbed in the intestine and is secreted in chylomicrons, which are then transferred to liver lysosomes. Most gamma-tocopherol is transferred to liver microsomes and is catabolized by cytochrome p450. Due to the hydrophobicity of gamma-tocopherol, a binding and transfer protein is plausible, but none have yet been isolated and characterized. We recently found that a ubiquitous cytosolic protein, saposin B, binds and transfers coenzyme Q10 (CoQ10), which is an essential factor for ATP production and an important antioxidant. Here, we report that saposin B also binds gamma-tocopherol, but not alpha-tocopherol, as efficiently as CoQ10 at pH 7.4. At acidic pH, saposin B binds gamma-tocopherol preferentially to CoQ10 and alpha-tocopherol. Furthermore, we confirmed that saposin B selectively binds gamma-tocopherol instead of CoQ10 and alpha-tocopherol at every pH between 5.4 and 8.0 when all three lipids are competing for binding. We detected gamma-tocopherol in human saposin B monoclonal antibody-induced immunoprecipitates from human urine, although the amount of gamma-tocopherol was much smaller than that of CoQ10. These results suggest that saposin B binds and transports gamma-tocopherol in human cells.