Researchers have answered a question that's dogged science for decades -- they've identified a receptor that allows vitamin A uptake into cells, according to a report in this week's Science. The study reveals evidence that a previously discovered but uncharacterized protein called STRA6 is a receptor for retinol-binding protein (RBP), which forms a complex with vitamin A. RBP's binding to STRA6 allows the attached vitamin A to be absorbed into the cell, according to the authors. "People have looked for a long time for a retinol-binding protein receptor and the data... have never been quite convincing," said Catharine Ross of Pennsylvania State University in University Park, who was not involved in the study. RBP binds to vitamin A stored in the liver and carries it through the blood to other organs. Although vitamin A itself can diffuse freely across cell membranes, the vitamin A-RBP complex cannot. Scientists have been...

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