Schematic representation of how MPO (green), particle surface and BSA (blue) concentration interplay to define the activity level of MPO.

(A) When purified MPO interacts with the particle surface its interaction modifies the conformation of the protein, which increase enzyme activity. (B) At medium protein concentration the MPO interaction with the surface is influenced by other proteins and is very active. (C) In high protein concentration media the MPO has less access to the surface and is less active either because of less MPO is bound to the surface or that the conformational change is less favorable in a crowded environment.