A natural biogenic nanozyme for scavenging superoxide radicals Biominerals, inorganic minerals produced by organisms, are known for their physical properties. Recent discoveries of enzyme-like activities in nanomaterials, called nanozymes, suggest that nano-biominerals may function as enzyme-like catalysts in cells. This study reports that the iron cores of biogenic ferritins act as natural nanozymes to scavenge superoxide radicals. Analysis of 18 ferritins from three living kingdoms shows that prokaryotic ferritins have higher superoxide-diminishing activity than eukaryotic ones. Differences in catalytic ability are due to changes in the iron/phosphate ratio in the iron core, determined by ferritin structures. Phosphate in the iron core changes the iron core from single crystalline to amorphous iron phosphate-like structure, decreasing its affinity to hydrogen protons, facilitating reaction with superoxide differently from ferric ions. Overexpression of high superoxide-diminishing ferritins in E. coli increases resistance to superoxide, while bacterioferritin knockout or human ferritin knock-in diminishes free radical tolerance, highlighting the physiological antioxidant role of these nanozymes. Biominerals are widely distributed and play important physiological roles in organisms. They are believed to participate in the origin of life and are integrated components of organisms. In the prebiotic era, inorganic minerals were thought to catalyze the synthesis and polymerization of initial biomolecules. Biominerals can catalyze primary organic synthesis, such as carbon fixation, and realize chiral molecule selection on chiral surfaces. Clay minerals can also catalyze the polymerization of peptides and RNA molecules. In modern organisms, biominerals are present in almost all species, such as carbonate and magnetite in bacteria, calcium oxalate in plants, and bones in animals. However, unlike their prebiotic roles, biominerals mainly serve physical support and protective functions. The catalytic role of biomineralized materials was little discussed until the discovery of enzyme-like activity in inorganic nanomaterials. These nanozymes have been widely studied in various areas, including environmental science and pharmaceutical industry. Nanozymes have catalytic activities and reaction kinetics similar to natural enzymes. Currently, various nanozymes have been developed, including single-atom nanozymes that can match natural horseradish peroxidase. These unique properties make nanozymes preferred enzyme mimics for applications in environmental protection, agriculture, disease diagnosis, and treatment. Natural nanozymes from biominerals, such as magnetosomes in magnetic bacteria, bio-interface mineral nanozymes in fungi and horse spleen ferritin, exhibit peroxidase-like activities. These nanozymes may have important physiological functions, such as antioxidant roles in protecting hosts from superoxide or hydroxyl radicals. Given the wide distribution of biominerals, itA natural biogenic nanozyme for scavenging superoxide radicals Biominerals, inorganic minerals produced by organisms, are known for their physical properties. Recent discoveries of enzyme-like activities in nanomaterials, called nanozymes, suggest that nano-biominerals may function as enzyme-like catalysts in cells. This study reports that the iron cores of biogenic ferritins act as natural nanozymes to scavenge superoxide radicals. Analysis of 18 ferritins from three living kingdoms shows that prokaryotic ferritins have higher superoxide-diminishing activity than eukaryotic ones. Differences in catalytic ability are due to changes in the iron/phosphate ratio in the iron core, determined by ferritin structures. Phosphate in the iron core changes the iron core from single crystalline to amorphous iron phosphate-like structure, decreasing its affinity to hydrogen protons, facilitating reaction with superoxide differently from ferric ions. Overexpression of high superoxide-diminishing ferritins in E. coli increases resistance to superoxide, while bacterioferritin knockout or human ferritin knock-in diminishes free radical tolerance, highlighting the physiological antioxidant role of these nanozymes. Biominerals are widely distributed and play important physiological roles in organisms. They are believed to participate in the origin of life and are integrated components of organisms. In the prebiotic era, inorganic minerals were thought to catalyze the synthesis and polymerization of initial biomolecules. Biominerals can catalyze primary organic synthesis, such as carbon fixation, and realize chiral molecule selection on chiral surfaces. Clay minerals can also catalyze the polymerization of peptides and RNA molecules. In modern organisms, biominerals are present in almost all species, such as carbonate and magnetite in bacteria, calcium oxalate in plants, and bones in animals. However, unlike their prebiotic roles, biominerals mainly serve physical support and protective functions. The catalytic role of biomineralized materials was little discussed until the discovery of enzyme-like activity in inorganic nanomaterials. These nanozymes have been widely studied in various areas, including environmental science and pharmaceutical industry. Nanozymes have catalytic activities and reaction kinetics similar to natural enzymes. Currently, various nanozymes have been developed, including single-atom nanozymes that can match natural horseradish peroxidase. These unique properties make nanozymes preferred enzyme mimics for applications in environmental protection, agriculture, disease diagnosis, and treatment. Natural nanozymes from biominerals, such as magnetosomes in magnetic bacteria, bio-interface mineral nanozymes in fungi and horse spleen ferritin, exhibit peroxidase-like activities. These nanozymes may have important physiological functions, such as antioxidant roles in protecting hosts from superoxide or hydroxyl radicals. Given the wide distribution of biominerals, it