Heme oxygenase is the first and rate limiting enzyme of the microsomal heme degradation pathway. Heme (iron protoporphyrin-IX), a co-factor and substrate of the enzyme, is catabolized through a process in which the key step involves the hydroxylation of the α-meso carbon of the porphyrin macrocycle by heme-bound oxygen. To study the mechanism of this reaction, we have formed the metastable O2 adduct of the heme—heme oxygenase complex and observed that its resonance Raman spectrum displays an oxygen isotope shift pattern unlike those of any other O2-bound heme proteins. Analysis of the spectra suggests that the Fe-O-O unit is highly bent, showing that steric interactions between the bound O2 and the residues of the distal pocket result in a unique mechanism of oxygen activation. We propose that the terminal oxygen atom is in van der Waals contact with an α-meso carbon of the porphyrin ring.
ASJC Scopus subject areas
- Colloid and Surface Chemistry