Heme degradation reaction of HutZ from Vibrio cholerae is regulated by the subunit–subunit interactions.

HutZ is a heme-degrading enzyme in Vibrio cholerae. It converts heme to biliverdin via verdoheme, suggesting that it follows the same reaction mechanism as that of mammalian heme oxygenase. However, none of the key intermediates have been identified. In this study, we applied steady-state and time-resolved UV-vis absorption and resonance Raman spectroscopy to study the reaction of heme-HutZ complex with H2O2 or ascorbic acid. We characterized three intermediates: oxyferrous heme, meso-hydroxyheme, and verdoheme complexes. Our data suport the view that HutZ degrades heme in a manner similar to mammalian heme oxygenase, despite their low sequence and structural homology.

HutZ is a heme-degrading enzyme. We found that the heme-degradation reaction by HutZ is inhibited by the iron chelators. Kinetic analysis of each heme-degradation step suggests that water molecules hydrogen bonded to Thr27 are involved in proton transfer to Fe(iii)-OO, and that this step is inhibited by iron chelators.