If the turn would describe an arc--not likely--the center of rotation would need to be at the center of that arc.  In other words, at the center of the circle that arc would be a part of.  I don't animate in Poser, but I doubt that you can change the center point during an animation.

The solution might be a lot of keyframes, more or less, depending the mode of animation, linear, interpolated, etc.  Both X and Z translations would need to be used along with the Y rotation.  Sounds messy ;)  Good luck!

John