Conformation of the abortifacient protein pinellin: a circular dichroic study.

The conformation of pinellin was studied by circular dichroism, which showed a minimum at 223 nm and a double maximum at 198-200 nm. The protein was rich in beta-sheet (about 40%) with little alpha-helix, based on current CD analyses. It was stable between pH4 and 10 beyond which it unfolded reversibly, but in alkaline solution, prolongly stored at, say, pH 12, it became irreversibly denatured. Thermal denaturation indicated a transition between 55 degrees and 68 degrees C; the solution at 80 degrees C was partially renatured upon air-cooling back to room temperature. Addition of sodium dodecyl sulfate caused a sharp increase in alpha-helix, which leveled off at 0.25 mM surfactant.