PBS works great. You alos have to add MgCl2, D-biotin and ATP (final conc. of 5 mM, 150 uM and 2 mM respectively).

You'll find some practical advice here:

http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=PMC4304673

Hope it helps!

I'd generally recommend to use HEPES or Tris buffers when working with MgCl2 as Mg - phosphate salts have low solubility. You definitely get precipitation when heating / autoclaving the Mg and phosphate and this will give problems.

Best Markus

Thank you Mr. A Martin and Mr. M Sack.