Molecular identification of adrenal inner zone antigen as a heme-binding protein

Li Min, Natallia V. Strushkevich, Ivan N. Harnastai, Hiroko Iwamoto, Andrei A. Gilep, Hiroshi Takemori, Sergey A. Usanov, Yasuki Nonaka, Hiroshi Hori, Gavin P. Vinson, Mitsuhiro Okamoto

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77 Citations (Scopus)


The adrenal inner zone antigen (IZA), which reacts specifically with a monoclonal antibody raised against the fasciculata and reticularis zones of the rat adrenal, was previously found to be identical with a protein variously named 25-Dx and membrane-associated progesterone receptor. IZA was purified as a glutathione 5-transferase-fused or His6-fused protein, and its molecular properties were studied. The UV-visible absorption and EPR spectra of the purified protein showed that IZA bound a heme chromophore in high-spin type. Analysis of the heme indicated that it is of the b type. Site-directed mutagenesis studies were performed to identify the amino-acid residues that bind the heme to the protein. The results suggest that two Tyr residues, Tyr107 and Tyr113, and a peptide stretch, D99-K102, were important for anchoring the heme into a hydrophobic pocket. The effect of IZA on the steroid 21-hydroxylation reaction was investigated in COS-7 cell expression systems. The results suggest that the coexistence of IZA with CYP21 enhances 21-hydroxylase activity.

Original languageEnglish
Pages (from-to)5832-5843
Number of pages12
JournalFEBS Journal
Issue number22
Publication statusPublished - Nov 2005
Externally publishedYes


  • Adrenal inner zone antigen
  • Heme-binding protein
  • Membrane-associated progesterone receptor
  • Steroidogenesis
  • Zonae fasciculata and reticularis


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