PathwayStep2622 PathwayStep2626 PathwayStep2625 PathwayStep2624 PathwayStep2623 Heme degradation GENE ONTOLOGYGO:0042167 Most of the heme degraded in humans comes from hemoglobin. Approximately 6-8 grams of hemoglobin is degraded daily which is equivalent to approximately 300 milligrams of heme per day. Heme is not recycled so it must be degraded and excreted. The iron, however, is conserved. There are two steps to heme degradation;<br>1. cleavage of the heme ring by a microsomal heme oxygenase producing biliverdin<br>2. biliverdin is reduced to bilirubin.<br>Bilirubin can then be conjugated with glucuronic acid and excreted. Pubmed12909459 Reactome Database ID Release 43189483 Reactome, http://www.reactome.org ReactomeREACT_22297 Reviewed: Sassa, S, 2007-01-24 10:18:36 Bilirubin monoglucuronide is conjugated to bilirubin diglucuronide Bilirubin translocates from the cytosol to the ER lumen Bilirubin forms a monoglucuronide The heme ring is cleaved by heme oxygenase Biliverdin is reduced to bilirubin