Reduction of Fe3+ in the endosome Authored: Stephan, R, 2010-07-14 EC Number: 1.16.1 Edited: Jassal, B, 2010-07-30 Pubmed16227996 Pubmed16609065 Reactome Database ID Release 43917811 Reactome, http://www.reactome.org ReactomeREACT_24919 Reviewed: D'Eustachio, P, 2010-11-05 The iron ions that are no longer bound to transferrin are reduced by the metalloreductase STEAP3, an endosomal membrane protein. The electron donor partner of the enzyme is unknown (Ohgami et al, 2005; Ohgami et al, 2006).