  We use ideas from kinetic proofreading, an error-correcting mechanism in
biology, to identify new kinetic regimes in non-equilibrium systems. These
regimes are defined by the sensitivity of the occupancy of a state of the
system to a change in its energy. In biological contexts, higher sensitivity
corresponds to stronger discrimination between molecular substrates with
different energetics competing in the same reaction. We study this
discriminatory ability in systems with discrete states that are connected by a
general network of transitions. We find multiple regimes of different
discriminatory ability when the energy of a given state of the network is
varied. Interestingly, the occupancy of the state can even increase with its
energy, corresponding to an "anti-proofreading" regime. The number and
properties of such discriminatory regimes are limited by the topology of the
network. Finally, we find that discriminatory regimes can be changed without
modifying any "hard-wired" structural aspects of the system but rather by
simply changing external chemical potentials.
