Detection and characterization of an ovine placental lactogen stable intermediate in the urea-induced unfolding process |
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Authors: | GD Cymes C Grosman JM Delfino C Wolfenstein-Todel |
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Affiliation: | Insituto de Química y Fisicoquímica Biológicas, Facultad de Farmacia y Bioquímica, UBA, Buenos Aires, Argentina. gdcymes@criba.edu.ar |
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Abstract: | The urea-induced equilibrium unfolding of ovine placental lactogen, purified from ovine placenta, was followed by size-exclusion chromatography, far-UV CD, and intrinsic tryptophan fluorescence. The data obtained by each of these methods showed a poor fit to a two-state model involving only a native and an unfolded form. A satisfactory fit required, instead, a model that involved a stable, partially folded form in addition to the native and unfolded ones. The results obtained from the best-fitting theoretical curves for the three-state model indicated that this intermediate state, which is the predominant species in solution at 3.6 M of urea activity, is compact, largely alpha-helical, and changes considerably the native-like tertiary packing around its tryptophan residues. These findings suggest that this stable intermediate exhibits properties similar to those that characterize the molten globule state. |
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