    1.1.1.145 | between pH 7.4 and 4.5, isoform 3betaHSD2 retains its primarily-helical character with a decrease in alpha-helical content at lower pH values, whereas the beta-sheet content remains unchanged throughout. Titrating the pH back to 7.4 restores the original conformation within 25 min. Metabolic conversion assays indicate peak 3betaHSD2 activity at pH 4.5 with 2fold more progesterone synthesized at pH 4.5 than at pH 3.5 and 7.4. Increasing the 3betaSD2 concentration from 1 to 40 microg results in a 7fold increase in progesterone at pH 4.5, but no change at pH 7.4. Incubation with guanidinum hydrochloride shows a three-step cooperative unfolding of 3betaHSD2 from pH 7.4 to 4.5, possibly due to the native state unfolding to the intermediate ion core state. With further decreases in pH, increasing concentrations of guanidinum hydrochloride lead to rapid two-step unfolding that may represent complete loss of structure |
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