Ferrireductasen

Ferrireductases are enzymes that catalyze the reduction of ferric iron (Fe3+) to ferrous iron (Fe2+). This one-electron transfer step is a critical prerequisite for iron uptake and mobilization in many organisms. Most ferrireductases are membrane-associated or soluble flavoproteins that use electron donors such as NADPH or NADH, and they often rely on cofactors like flavin adenine dinucleotide (FAD) or flavin mononucleotide (FMN). In some systems, multicopper oxidases participate in related redox processes at the cell surface or within intracellular membranes.

Across kingdoms, ferrireductases support iron acquisition by enabling the conversion of iron in form that transporters can utilize. In plants, ferric chelate reductases such as FRO2 reside in the root plasma membrane and reduce Fe3+-chelates to Fe2+, which is then taken up by iron transporters like IRT1. In yeast, ferric reductases Fre1 and Fre2 reduce extracellular Fe3+ to Fe2+ to supply permeases for uptake. In mammals, the intestinal epithelium uses duodenal cytochrome b (Dcytb, CYBRD1) as a ferrireductase to generate Fe2+ for absorption via DMT1, while intracellular ferrireductases of the STEAP family (notably STEAP3) reduce ferric iron within endosomes during transferrin-derived iron release.

Functional diversity and localization reflect the central role of ferrireductases in iron homeostasis. They contribute to nutrient uptake, storage, and recovery processes, and their activity influences conditions related to iron deficiency and iron overload. The term encompasses a range of enzymes with similar redox goals but differing cellular contexts and partners.