ferrireductase

Ferrireductase is an enzyme that catalyzes the reduction of ferric iron (Fe3+) to ferrous iron (Fe2+). This redox reaction is a key step in iron acquisition, mobilization, and intracellular iron utilization across a range of organisms. Ferrireductases are often membrane-associated proteins that operate in conjunction with iron transport systems to enable the uptake of iron from extracellular sources.

In animals and humans, ferrireductase activity is exemplified by duodenal cytochrome b (Dcytb), a ferrireductase located on the apical surface of enterocytes in the small intestine. Dcytb uses electron donors such as ascorbate or NADPH to reduce dietary Fe3+ to Fe2+, which is then transported into cells by the divalent metal transporter 1 (DMT1). Ferrireductase activity also contributes to iron recycling and homeostasis in various tissues.

In plants, ferric chelate reductases, members of the FRO (Ferric Reduction Oxidase) family, are plasma membrane enzymes that reduce Fe3+-chelates in the rhizosphere to Fe2+. This reduction is a prerequisite for iron uptake through transporters in the root epidermis. Plants upregulate ferrireductase activity under iron deficiency to enhance iron acquisition and maintain growth, a response linked to broader regulatory networks controlling iron homeostasis.

In microorganisms, ferrireductases facilitate iron uptake under limiting conditions by reducing extracellular Fe3+ to Fe2+, enabling transport via dedicated or general metal transport systems. These enzymes display diversity in cofactor usage and membrane localization, reflecting adaptation to different ecological niches.

Overall, ferrireductases play a central role in iron metabolism by converting ferric to ferrous iron, thereby enabling cellular uptake, distribution, and utilization of this essential micronutrient.