  We determine both barrier heights and prefactors for protein folding by
applying constraints determined from experimental rate measurements to a
Kramers theory for folding rate. The theoretical values are required to match
the experimental values at two conditions of temperature and denaturant that
induce the same stability. Several expressions for the prefactor in the Kramers
rate equation are examined: a random energy approximation, a correlated energy
approximation, and an approximation using a single Arrhenius activation energy.
Barriers and prefactors are generally found to be large as a result of
implementing this recipe, i.e. the folding landscape is cooperative and smooth.
Interestingly, a prefactor with a single Arrhenius activation energy admits no
formal solution.
