Recently I've spent a great deal of time thinking about enzyme diffusion in cytoplasm. One thing that keeps me awake at night is the constant referral to cytoplasm as a non-Newtonian fluid (which it surely is when looking at it as a whole), and the implications this has for the diffusive properties of singular enzymes.
If I think about a single enzyme in the cytoplasm with its immediate surroundings, I would expect to find the protein with its solvation shells, and only a few non-water components. In this context I'm unable to understand how this single enzyme could be thought to be in a non-Newtonian medium.
Furthermore, when thinking about the diffusion of the enzyme, quite a few authors refer to the Scallop theorem, and define it in the context of non-Newtonian fluids. If the enzyme is mostly surrounded by water molecules, and only occasionally runs in to other proteins or peptides, shouldn't the protein be considered to reside in a Newtonian medium?
Shortly put: How far down can you go until the classification between Newtonian and non-Newtonian fluids starts to break down?