metalloreductase

Metalloreductase refers to enzymes that catalyze the reduction of metal ions by transferring electrons from electron donors such as NADH or NADPH through cellular electron transport chains. These enzymes participate in metal respiration, metal homeostasis, and detoxification, and are found in various organisms including bacteria, archaea, fungi, and plants. Metalloreductases may be soluble cytosolic proteins, periplasmic proteins, or membrane-associated complexes.

Common types include ferrireductases, which reduce Fe3+ to Fe2+ to facilitate iron uptake or respiration; chromate reductases that convert soluble Cr(VI) to Cr(III); mercuric reductases that reduce Hg2+ to elemental mercury; and arsenate reductases that convert arsenate to arsenite as part of detox pathways. These enzymes often rely on cofactors such as NADPH, FAD, heme, or cytochromes and may function directly at the membrane or via transfer partners in electron transport chains.

In bacteria such as Shewanella oneidensis and Geobacter species, metalloreductases participate in extracellular electron transfer, using outer-membrane multiheme cytochromes to reduce insoluble metal oxides. In plants, ferric chelate reductases of the FRO family are plasma membrane enzymes that reduce Fe3+-chelate complexes as a prerequisite for iron uptake. In fungi, yeast, and others, reductases contribute to iron acquisition and detoxification of metals.

Metalloreductases are of interest for bioremediation and biogeochemical cycling of metals, as well as applications in bioelectrochemical systems and metal recovery. Understanding these enzymes aids in elucidating microbial metal metabolism and in developing strategies to mitigate metal contamination or recover valuable metals from wastes.