Protein shells have been used as nano-platforms for the synthesis of metallic nanoparticles for their biomedical and biocatalytic applications. However, it is challenging to maximize the catalytic activity of nanoparticles encapsulated by protein shells, as little research exists regarding their effect on the catalytic activities or physicochemical properties of nanoparticles. In this study, we used the following three proteins to synthesize platinum nanoparticles: aminopeptidase PepA, serine endoprotease DegP, and Clp protease. We then compared the catalytic properties of these protein-shelled platinum nanoparticles as scavengers of reactive oxygen species. These protein-shelled platinum nanoparticles displayed the catalase- and superoxide dismutase-like activities by quenching H₂O₂ and O₂⁻, respectively. However, the resulting particle's size and activity depended on the particular protein shell. These results proved that the catalytic activity of protein-shelled platinum nanoparticles is greatly affected by the physicochemical properties of their protein shells. Collectively, current study indicates that protein shells are important determinants for the physical and catalytic properties of platinum nanoparticles and it is necessary to screen protein shells to optimize their functionality. Furthermore, considering the reduced cell toxicity of protein-shelled platinum nanoparticles compared to those synthesized by chemical stabilizers, it is suggested that they can serve as an antioxidant for biomedical purposes.