title: Heme oxygenase-2 is a hemoprotein and binds heme through heme regulatory motifs that are not involved in heme catalysis.
abstract: The heme oxygenase (HO) system degrades heme to biliverdin and CO and releases chelated iron. In the primary sequence of the constitutive form, HO-2, there are three potential heme binding sites: two heme regulatory motifs (HRMs) with the absolutely conserved Cys-Pro pair, and a conserved 24-residue heme catalytic pocket with a histidine residue, His151 in rat HO-2. The visible and pyridine hemochromogen spectra suggest that the Escherichia coli expressed purified HO-2 is a hemoprotein. The absorption spectrum, heme fluorescence quenching, and heme titration analysis of the wild-type protein versus those of purified double cysteine mutant (Cys264/Cys281 --> Ala/Ala) suggest a role of the HRMs in heme binding. While the His151 --> Ala mutation inactivates HO-2, Cys264 --> Ala and Cys281 --> Ala mutations individually or together (HO-2 mut) do not decrease HO activity. Also, Pro265 --> Ala or Pro282 --> Ala mutation does not alter HO-2 activity. Northern blot analysis of ptk cells indicates that HO-2 mRNA is not regulated by heme. The findings, together with other salient features of HO-2 and the ability of heme-protein complexes to generate oxygen radicals, are consistent with HO-2, like five other HRM-containing proteins, having a regulatory function in the cell.
authors.affiliation: Department of Biochemistry, University of Rochester School of Medicine, Rochester, New York 14642, USA.
authors.forename: W K
authors.initials: WK
authors.lastname: McCoubrey
authors.forename: T J
authors.initials: TJ
authors.lastname: Huang
authors.forename: M D
authors.initials: MD
authors.lastname: Maines
mesh_terms: D000818:Animals; D015152:Blotting, Northern; D002478:Cells, Cultured; D004591:Electrophoresis, Polyacrylamide Gel; D006418:Heme / Q000378:metabolism*; D006419:Heme Oxygenase (Decyclizing) / Q000378:metabolism*; D007527:Isoenzymes / Q000378:metabolism*; D016297:Mutagenesis, Site-Directed; D011487:Protein Conformation; D051381:Rats; D013050:Spectrometry, Fluorescence; D013054:Spectrophotometry, Atomic
chemical_list: D007527:Isoenzymes; D006418:Heme; D006419:Heme Oxygenase (Decyclizing); C105245:heme oxygenase-2