期刊名称：Journal of Clinical Biochemistry and Nutrition
印刷版ISSN：0912-0009
电子版ISSN：1880-5086
出版年度：2008
卷号：42
期号：2
页码：167-174
DOI：10.3164/jcbn.2008024
出版社：The Society for Free Radical Research Japan
摘要：Coenzyme Q10 (CoQ10) is essential for ATP production in the mitochondria, and is an important antioxidant in every biomembrane and lipoprotein. Due to its hydrophobicity, a binding and transfer protein for CoQ10 is plausible, but none have yet been isolated and characterized. Here we purified a CoQ10-binding protein from human urine and identified it to be saposin B, a housekeeping protein necessary for sphingolipid hydrolysis in lysosomes. We confirmed that cellular saposin B binds CoQ10 in human sperm and the hepatoma cell line HepG2 by using saposin B monoclonal antibody. The molar ratios of CoQ10 to saposin B were estimated to be 0.22 in urine, 0.003 in HepG2, and 0.12 in sperm. We then confirmed that aqueous saposin B extracts CoQ10 from hexane to form a saposin B-CoQ10 complex. Lipid binding affinity to saposin B decreased in the following order: CoQ10>CoQ9>CoQ7>>α-tocopherol>>cholesterol (no binding). The CoQ10-binding affinity to saposin B increased with pH, with maximal binding seen at pH 7.4. On the other hand, the CoQ10-donating activity of the saposin B-CoQ10 complex to erythrocyte ghost membranes increased with decreasing pH. These results suggest that saposin B binds and transports CoQ10 in human cells.
