  Protein aggregation in the form of amyloid fibrils has important biological
and technological implications. Although the self-assembly process is highly
efficient, aggregates not in the fibrillar form would also occur and it is
important to include these disordered species when discussing the thermodynamic
equilibrium behavior of the system. Here, we initiate such a task by
considering a mixture of monomeric proteins and the corresponding aggregates in
the disordered form (micelles) and in the fibrillar form (amyloid fibrils).
Starting with a model on the respective binding free energies for these
species, we calculate their concentrations at thermal equilibrium. We then
discuss how the incorporation of the disordered structure furthers our
understanding on the various amyloid promoting factors observed empirically,
and on the kinetics of fibrilization.
