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Hydrophobic vitamins are transported in human plasma and extravascular fluids by carrier proteins. No specific protein has been described so far for vitamin E, which plays a crucial role in protecting against oxidative damage and disease. We report here the purification of a 75-kDa glycoprotein with vitamin E-binding properties by stepwise chromatography of lipoprotein-depleted human plasma and monitoring of vitamin E (α-tocopherol)-binding activity. Partial sequencing identified this protein as afamin, a previously described member of the albumin gene family with four or five potential N-glycosylation sites. Glycosylation analysis indicated that >90% of the glycans were sialylated biantennary complex structures. The vitamin E-binding properties were confirmed using recombinantly expressed afamin. Qualitative and quantitative analysis of plasma and extravascular fluids revealed an abundant presence of this protein not only in plasma (59.8 ± 13.3 μg/mL) but also in extravascular fluids such as follicular (34.4 ± 12.7 μg/mL) and cerebrospinal (0.28 ± 0.16 μg/mL) fluids, suggesting potential roles for afamin in fertility and neuroprotection. Afamin is partly (13%) bound to plasma lipoproteins. Afamin and vitamin E concentrations significantly correlate in follicular and cerebrospinal fluids but not in plasma. The vitamin E association of afamin in follicular fluid was directly demonstrated by gel filtration chromatography and immunoprecipitation which complements the in vitro findings for purified native and recombinant afamin. Keywords: afamin • vitamin E binding • glycosylation analysis • 2-D electrophoresis • recombinant expression • quantification more...