Heme oxygenase cleaves the heme ring at the alpha methene bridge to form biliverdin. Biliverdin is subsequently converted to bilirubin by biliverdin reductase. Under physiological conditions, the activity of heme oxygenase is highest in the spleen, where senescent erythrocytes are sequestrated and destroyed.
[1] "Human heme oxygenase cDNA and induction of its mRNA by hemin."Yoshida T., Biro P., Cohen T., Mueller R.M., Shibahara S.Eur. J. Biochem. 171:457-461(1988) [2] "A genome annotation-driven approach to cloning the human ORFeome."