The long search for an intestinal mammalian heme transporter has revealed a protein that is upregulated by hypoxia, and not iron stores, according to a study in Cell by Andrew McKie and colleagues at Kings College London.

The work adds fuel to a debate over whether heme uptake is regulated by iron levels, said Aliye Uc of the University of Iowa Children's Hospital, who did not participate in the study.

The researchers subtracted the ileum cDNA library from that of the duodenum, the primary site of intestinal heme absorption, in severely anemic mice. They honed in the protein, heme carrier protein 1 (HCP1), determining its homology to bacterial metal-tetracycline transporters and finding that its transcription is regulated by hypoxia, which is known to stimulate iron absorption.

The researchers expressed the putative transporter in xenopus oocyte cells and infected cultured HeLa cells with HCP1 adenovirus, then exposed the cell lines to...

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