Crystallographic studies of heme oxygenase complexed with an unstable reaction intermediate, verdoheme

This article discusses the accuracy of X-ray structural studies of heme oxygenase (HO) in complex with an unstable intermediate, verdoheme. Heme degradation by HO proceeds through three successive steps of O-2 activation. The mechanism of the third step, the ring opening of verdoheme, has been the least understood. Recent structural studies of the verdoheme-HO complex provide detailed information concerning this mechanism. Due to X-ray-induced photoreduction and the instability of verdoheme, it has been difficult to obtain an accurate structure for the ferrous verdoheme-HO complex. Therefore, accurate structural studies, including analysis of the electronic state of the verdoheme-HO complex, are needed to elucidate the proper reaction mechanism. (C) 2012 Elsevier Inc. All rights reserved.