Heme oxygenase-2. Properties of the heme complex of the purified tryptic fragment of recombinant human heme oxygenase-2.
Recombinant human microsomal heme oxygenase-2 was expressed in Escherichia coli. Tryptic digestion of the membrane fraction, in which the wild-type enzyme was localized, yielded a soluble tryptic peptide of 28 kDa, which retained the ability to accept electrons from NADPH-cytochrome P-450 reductase and the enzymatic activity for conversion of heme to biliverdin. The tryptic fragment, when purified to apparent homogeneity, bound one equivalent of heme to form a substrate-enzyme complex that had spectroscopic properties characteristic of heme proteins, such as myoglobin and hemoglobin. Optical absorption, Raman scattering, and EPR studies of the heme-tryptic fragment complex revealed that the ferric heme was six coordinate high spin at neutral pH and six coordinate low spin at alkaline pH, with a pK alpha value of 8.5. EPR and Raman scattering studies indicated that a neutral imidazole of a histidine residue served as the proximal ligand in the heme-heme oxygenase-2 fragment complex. The reaction with hydrogen peroxide converted the heme of the heme oxygenase-2 fragment complex into a verdoheme-like intermediate, while the reaction with m-chloroperbenzoic acid yielded a oxoferryl species. These spectroscopic properties are similar to those obtained for heme oxygenase-1, and thus the catalytic mechanism of heme oxygenase-2 appears to be similar to that of heme oxygenase-1.
Ishikawa
K
K
Department of Biochemistry, Yamagata University School of Medicine, Japan.
Takeuchi
N
N
Takahashi
S
S
Matera
K M
KM
Sato
M
M
Shibahara
S
S
Rousseau
D L
DL
Ikeda-Saito
M
M
Yoshida
T
T
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D003001:Cloning, Molecular; D018076:DNA, Complementary; D004578:Electron Spin Resonance Spectroscopy; D004926:Escherichia coli; D006418:Heme / Q000737:chemistry / Q000378:metabolism*; D006419:Heme Oxygenase (Decyclizing) / Q000096:biosynthesis / Q000737:chemistry* / Q000378:metabolism*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007527:Isoenzymes / Q000096:biosynthesis / Q000737:chemistry / Q000378:metabolism; D007700:Kinetics; D008861:Microsomes / Q000201:enzymology; D008969:Molecular Sequence Data; D009838:Oligodeoxyribonucleotides; D010446:Peptide Fragments / Q000737:chemistry / Q000378:metabolism*; D011487:Protein Conformation; D011817:Rabbits; D051381:Rats; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D013053:Spectrophotometry; D013059:Spectrum Analysis, Raman; D014357:Trypsin
D018076:DNA, Complementary; D007527:Isoenzymes; D009838:Oligodeoxyribonucleotides; D010446:Peptide Fragments; D011994:Recombinant Proteins; D006418:Heme; D006419:Heme Oxygenase (Decyclizing); D014357:Trypsin