[PyMOL] rearranging the coordinates of a PDB file

[Vanessa Oklejas]

Hi all,

I'm a new user of MacPyMOL. I would like to modify the coordinates of 
my PDB file such that the origin (0,0,0) is centered at the mid-point 
of a molecular bond.  I've found that I can make (and save) changes 
in the Z and Y coordinates (in 3 button editing mode moving the 
structure up/down (Z), left/right(Y)), but I cannot really reliably 
shift the X coordinate reliably using the mouse.

So I have 3 questions:

(1)  Are there commands that I can type such that I can shift the 
coordinate for the entire PDB file without using the mouse?

(2) If the mouse is the only way I can shift coordinates, then how do 
I use the mouse so that I can change the X-coordinate?

(3) What does the origin command do?

Thanks,
Vanessa