  It is shown that the kinetics of time-reversible chemical reactions having
the same equilibrium constant but different initial conditions are closely
related to one another by a directly measurable symmetry relation analogous to
chemical detailed balance. In contrast to detailed balance, however, this
relation does not require knowledge of the elementary steps that underlie the
reaction, and remains valid in regimes where the concept of rate constants is
ill-defined, such as at very short times and in the presence of low activation
barriers. Numerical simulations of a model of isomerization in solution are
provided to illustrate the symmetry under such conditions, and potential
applications in protein folding-unfolding are pointed out.
