  A simple model of an active colloid consisting of dumbbell-shaped particles
that cyclically change their length without propelling themselves is proposed
and analyzed. At nanoscales, it represents an idealization for bacterial
cytoplasm or for a biomembrane with active protein inclusions. Our numerical
simulations demonstrate that non-equilibrium conformational activity of
particles can strongly affect diffusion and structural relaxation: while a
passive colloid behaves as a glass, it gets progressively fluidized when the
activity is turned on. Qualitatively, this agrees with experimental results on
optical tracking of probe particles in bacterial and yeast cells where
metabolism-induced fluidization of cytoplasm was observed.
