Journal of Biochemistry Advance Access originally published online on October 15, 2007
Journal of Biochemistry 2007 142(6):699-705; doi:10.1093/jb/mvm185
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© 2007 The Japanese Biochemical Society.
Involvement of 101F6, a Homologue of Cytochrome b561, in the Reduction of Ferric Ions
1Department of Biotechnology, Kyoto Institute of Technology, Kyoto 606-8585; 2Food Science and Nutrition, Nara Women's University, Nara 622-8506; and 3Insect Biomedical Center, Kyoto Institute of Technology, Kyoto 606-8585, Japan
*To whom correspondence should be addressed. Tel: 81-75-724-7789, Fax: 81-75-724-7760, E-mail: taketani{at}kit.ac.jp
Received July 30, 2007; Accepted September 14, 2007
| Abstract |
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We have isolated and characterized a small transmembrane protein, called 101F6, showing high sequence homology to cytochrome b561, a protein containing two binding sites for haem. The newly identified 101F6 contains six membrane spanning domains in which conserved histidine residues are located, and has a molecular mass of 25 kDa. When the haem-binding with bacterial expressed 101F6 was examined, the protein bound haem and the deletion of one histidine residue at 149 caused a loss of the binding. 101F6 mRNA was expressed widely in various tissues, and especially abundant in liver, kidney and lung. It was also expressed in several cultured cell lines. The protein expressed from the 101F6 cDNA in Balb/3T3 cells was about 25 kDa in size and was localized in small vesicles, including endosomes and endoplasmic reticulum of the perinuclear region. Comparison of the location of 101F6 with that of transferrin receptor-1 revealed that the localization of 101F6 in small vesicles was not always the same as the localization of transferrin receptor-1, but was similar to that of haem oxygenase-1. The other homologue to cytochrome b561, SDR-2 was also expressed in the small vesicles similar to the location of 101F6. Finally, reduction of ferric ions as well as of azo-dye increased with 101F6- or SDR-2-expressing cells. Thus, both 101F6 and SDR-2 were localized in small vesicles of cells and played roles in the reduction of ferric ions.
Key Words: 101F6, cytochrome b561, ferric reductase, haemoprotein, SDR-2
Abbreviations: Dcytb, duodenal cytochrome b561; SDR-2, stromal cell-derived receptor-2; FCS, fetal calf serum; SDS, sodium dodecyl sulfate; DMEM, Dulbecco's modified Eagle's medium; PBS, phosphate-buffered saline; GST, glutathione S-transferase