Source of pure PEG?

Andy Arvai arvai at
Wed May 12 18:03:04 EST 1993

We have a protein which we are trying to crystallize. There is 5mM
magnesium in the protein solution. We have crystallized this in PEG 4k
after dialyzing out the magnesium. However it is known that magnesium is
required for activity and therefore we would like to crystallize
it with magnesium. The problem is that the PEG 4k's we have tried have
phosphate in them and this causes magnesium phosphate crystals to
form. Phosphate is present because PEG is frequently neutralized by
the addition phosphoric acid.

Does anybody have a source of phosphate-free PEG or know of a good way
to purify the PEG?

Andy Arvai 
The Scripps Research Institute
arvai at 

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