In control reactions, no reaction occurred without monomer, whereas reactions in which either mPEG-BiB, NaAsc, or Mb were omitted proceeded with a low monomer consumption of <20%. Thus, a low level of blank reaction happened, but the initiator, oxidising agent, and the metallo-protein are necessary for the reaction to proceed to high conversions (Table ). The organic co-solvent DMF was necessary as well, likely as stabilizer for the growing chains. Furthermore, polymerisations were unsuccessful when they were carried out in pure PBS or in a 100 mM NaBr solution in deionised water, indicating that both the salts in the PBS buffer and the NaBr were required for the polymerisation to happen, most likely because the buffer maintained the pH and NaBr maintained an excess of halides that is need for efficient ATRP in aqueous conditions. 95