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Coenzyme Q10-Binding/Transfer Protein Saposin B also Binds gamma-Tocopherol.

Jin G, Horinouchi R, Sagawa T, Orimo N, Kubo H, Yoshimura S, Fujisawa A, Kashiba M, Yamamoto Y - J Clin Biochem Nutr (2008)

Bottom Line: 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.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.

View Article: PubMed Central - PubMed

Affiliation: School of Bionics, Tokyo University of Technology, 1404-1 Katakura-cho, Hachioji, Tokyo 192-0982, Japan.

ABSTRACT
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.

No MeSH data available.


Related in: MedlinePlus

Binding affinity of CoQ10, CoQ7, α-Toc, and γ-Toc to saposin B. Each lipid (10 mM) in hexane solution was incubated independently with aqueous 0.5 µM saposin B (pH = 7.4) for 5 min and amounts of lipids bound to saposin B were measured. All experiments were repeated 3–6 times and means ± SD are shown. * and *** indicate significant differences (p<0.05 and 0.001, respectively) compared to values for γ-Toc. NS: not significant.
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Figure 2: Binding affinity of CoQ10, CoQ7, α-Toc, and γ-Toc to saposin B. Each lipid (10 mM) in hexane solution was incubated independently with aqueous 0.5 µM saposin B (pH = 7.4) for 5 min and amounts of lipids bound to saposin B were measured. All experiments were repeated 3–6 times and means ± SD are shown. * and *** indicate significant differences (p<0.05 and 0.001, respectively) compared to values for γ-Toc. NS: not significant.

Mentions: The chemical structures of CoQ10, CoQ7, α-Toc, and γ-Toc are shown in Fig. 1. We compared the binding affinities of these lipids to saposin B by independently incubating 10 mM hexane solutions with aqueous CoQ10-free saposin B (0.5 µM) solution (pH 7.4) for 5 min, and then analyzing lipid contents in aqueous saposin B solution. Fig. 2 shows the binding affinity of lipids, which decreases in the order of CoQ10>CoQ7>>α-Toc, thus suggesting that tail length is an important factor in determining binding affinity. It is therefore surprising that saposin B binds γ-Toc as efficiently as CoQ10 (Fig. 2) despite, the much shorter tail length of γ-Toc. Saposin B binds γ-Toc much more strongly than α-Toc (Fig. 2), suggesting that the methyl group at the C-5 position of α-Toc interferes with binding to saposin B. These results suggest that saposin B has a binding site for γ-Toc.


Coenzyme Q10-Binding/Transfer Protein Saposin B also Binds gamma-Tocopherol.

Jin G, Horinouchi R, Sagawa T, Orimo N, Kubo H, Yoshimura S, Fujisawa A, Kashiba M, Yamamoto Y - J Clin Biochem Nutr (2008)

Binding affinity of CoQ10, CoQ7, α-Toc, and γ-Toc to saposin B. Each lipid (10 mM) in hexane solution was incubated independently with aqueous 0.5 µM saposin B (pH = 7.4) for 5 min and amounts of lipids bound to saposin B were measured. All experiments were repeated 3–6 times and means ± SD are shown. * and *** indicate significant differences (p<0.05 and 0.001, respectively) compared to values for γ-Toc. NS: not significant.
© Copyright Policy - open-access
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2533725&req=5

Figure 2: Binding affinity of CoQ10, CoQ7, α-Toc, and γ-Toc to saposin B. Each lipid (10 mM) in hexane solution was incubated independently with aqueous 0.5 µM saposin B (pH = 7.4) for 5 min and amounts of lipids bound to saposin B were measured. All experiments were repeated 3–6 times and means ± SD are shown. * and *** indicate significant differences (p<0.05 and 0.001, respectively) compared to values for γ-Toc. NS: not significant.
Mentions: The chemical structures of CoQ10, CoQ7, α-Toc, and γ-Toc are shown in Fig. 1. We compared the binding affinities of these lipids to saposin B by independently incubating 10 mM hexane solutions with aqueous CoQ10-free saposin B (0.5 µM) solution (pH 7.4) for 5 min, and then analyzing lipid contents in aqueous saposin B solution. Fig. 2 shows the binding affinity of lipids, which decreases in the order of CoQ10>CoQ7>>α-Toc, thus suggesting that tail length is an important factor in determining binding affinity. It is therefore surprising that saposin B binds γ-Toc as efficiently as CoQ10 (Fig. 2) despite, the much shorter tail length of γ-Toc. Saposin B binds γ-Toc much more strongly than α-Toc (Fig. 2), suggesting that the methyl group at the C-5 position of α-Toc interferes with binding to saposin B. These results suggest that saposin B has a binding site for γ-Toc.

Bottom Line: 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.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.

View Article: PubMed Central - PubMed

Affiliation: School of Bionics, Tokyo University of Technology, 1404-1 Katakura-cho, Hachioji, Tokyo 192-0982, Japan.

ABSTRACT
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.

No MeSH data available.


Related in: MedlinePlus