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Biological Activity: mPEG5000-Mal (mPEG5000-Maleimide) is a PEG-derived selective covalent binding agent for sulfhydryl groups (RSGs), which can form irreversible thioether bonds with sulfhydryl groups under near-neutral conditions via the maleimide group. The mechanism of action of mPEG5000-Mal can be divided into two categories: firstly, as an enzyme modifier, it binds to target proteins through hydrophobic interactions, hydrogen bonds, and van der Waals forces, altering the protein's secondary structure; secondly, as a nanoparticle surface modifier, it covalently binds to sulfhydryl groups on the surface of red blood cells, changing the surface properties and morphology of the red blood cells, leading to their phagocytosis by macrophages of the reticuloendothelial system. mPEG5000-Mal can react with free cysteine in proteins, increasing the apparent molecular weight of the modified protein by 10-15 kDa for detection purposes. mPEG5000-Mal can enhance the thermal stability and catalytic activity of enzymes, and improve the macrophage targeting of nanoparticles, enabling targeted drug delivery. mPEG5000-Mal can be applied in enzyme engineering research in the food industry and in oncology, assisting radiotherapy by inhibiting tumor-associated macrophage infiltration and enhancing anti-tumor immune responses^[1][2][3][4].