Heme oxygenase-2. Properties of the heme complex of the purified tryptic fragment of recombinant human heme oxygenase-2

K. Ishikawa, N. Takeuchi, S. Takahashi, K. M. Matera, M. Sato, S. Shibahara, D. L. Rousseau, M. Ikeda-Saito, T. Yoshida

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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 home to form a substrate-enzyme complex that had spectroscopic properties characteristic of home 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(a) 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 home 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 home oxygenase-1, and thus the catalytic mechanism of heme oxygenase-2 appears to be similar to that of home oxygenase-1.

Original languageEnglish
Pages (from-to)6345-6350
Number of pages6
JournalJournal of Biological Chemistry
Issue number11
Publication statusPublished - 1995


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