Ins and outs of cellular cobalamin transport

Quite a bit is now known about the complex mechanisms underlying how Cbl gets into cells. Just how the vitamin gets out for recycling remained a mystery until the findings by Beedholm-Ebsen and colleagues. In their article in this issue of Blood, cellular egress of Cbl is shown to occur by transport of "free" Cbl via the ABC drug transporter, ABCC1 (also known as the MRP1), present in the basolateral membrane of intestinal epithelium and in other cells.