  We generalize the concept of charge regulation of ionic solutions, and apply
it to complex fluids with mobile macro-ions having internal non-electrostatic
degrees of freedom. The suggested framework provides a convenient tool for
investigating systems where mobile macro-ions can self-regulate their charge
(e.g., proteins). We show that even within a simplified charge-regulation
model, the charge dissociation equilibrium results in different and notable
properties. Consequences of the charge regulation include a positional
dependence of the effective charge of the macro-ions, a non-monotonic
dependence of the effective Debye screening length on the concentration of the
monovalent salt, a modification of the electric double-layer structure, and
buffering by the macro-ions of the background electrolyte.
