A recombinant bovine α-lactalbumin, possessing an additional N-terminal methionyl residue, was expressed in Escherichia coli. In order to address the effects of the N-terminal methionyl residue on conformational stability, the thermal stability of the recombinant α-lactalbumin was investigated by measuring temperature-dependence of circular dichroism spectra, and it was compared with that of authentic α-lactalbumin from bovine milk. The thermal stability of the recombinant α-lactalbumin was

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... ificantly lower than that of authentic α-lactalbumin. The enthalpy change of unfolding of the recombinant protein was found to be the same as that of the authentic one when compared at the same temperature. Therefore, the N-terminal methionyl residue seems to destabilize the conformation of recombinant α-lactalbumin through some entropic effects.