The trifluoroethanol (TFE)-induced structural changes
of two proteins widely used in folding experiments, bovine
α-lactalbumin, and bovine pancreatic ribonuclease A,
have been investigated. The experiments were performed
using circular dichroism spectroscopy in the far- and near-UV
region to monitor changes in the secondary and tertiary
structures, respectively, and dynamic light scattering
to measure the hydrodynamic dimensions and the intermolecular
interactions of the proteins in different conformational
states. Both proteins behave rather differently under the
influence of TFE: α-lactalbumin exhibits a molten globule
state at low TFE concentrations before it reaches the so-called
TFE state, whereas ribonuclease A is directly transformed
into the TFE state at TFE concentrations above 40% (v/v).
The properties of the TFE-induced states are compared with
those of equilibrium and kinetic intermediate states known
from previous work to rationalize the use of TFE in yielding
information about the folding of proteins. Additionally,
we report on the properties of TFE/water and TFE/buffer
mixtures derived from dynamic light scattering investigations
under conditions used in our experiments.