The effect of pressure on the unfolding of bovine
α-lactalbumin was investigated by ultraviolet absorption
methods. The change of molar volume associated with unfolding,
ΔV, was measured in the presence or absence
of guanidine hydrochloride at pH 7. The ΔV
was estimated to be −63 cm3/mol in the
absence of a chemical denaturant. While in the presence
of guanidine hydrochloride (GuHCl), it was found that ΔV
was −66 cm3/mol at 25 °C and was independent
of the concentration of GuHCl, despite the fact that the
molten globule fraction in the total unfolding product
decreased with the increase of GuHCl concentration. The
results indicate that the volume of α-lactalbumin only
changes at the transition from a native to a molten globule
state, and almost no volume change has been found during
the transition from a molten globule to the unfolded state.