Duodenal cytochrome B has been identified as the reductase enzyme

Enzyme

Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...

 which catalyzes

Catalysis

Catalysis is the change in rate of a chemical reaction due to the participation of a substance called a catalyst. Unlike other reagents that participate in the chemical reaction, a catalyst is not consumed by the reaction itself. A catalyst may participate in multiple chemical transformations....

 the reduction of Fe³⁺ to Fe²⁺ in the process of iron absorption in the duodenum

Duodenum

The duodenum is the first section of the small intestine in most higher vertebrates, including mammals, reptiles, and birds. In fish, the divisions of the small intestine are not as clear and the terms anterior intestine or proximal intestine may be used instead of duodenum...

 of mammals. According to research carried out, it appears that Dcytb upregulation is controlled by a number of independent stimulators or inhibitors of iron absorption. Furthermore, Dcytb has also been shown to exist in other tissues besides the apical region of the duodenum; and as such, it is believed to play a major role in iron metabolism in tissues.