We had a similar experience a few years ago. In our case, the adventitious ligand was L-lactate, which happens to be a competitive inhibitor of our enzyme. We used using L-lactate dehydrogenase assays to show that several commercially available PEGs contain L-lactate. We also think that acetate ions are present in PEGs, based on crystallographic data. See these papers for the full story:
M. Zhang and J.J. Tanner Detection of L-lactate in polyethylene glycol solutions confirms the identity of the active-site ligand in a proline dehydrogenase structure. Acta Crystallogr. (2004) D60, 985-986 PMID: 15103160 M. Zhang, T.A. White, J.P. Schuermann, B.A. Baban, D.F. Becker, and J. J. Tanner Structures of the Escherichia coli PutA proline dehydrogenase domain in complex with competitive inhibitors. Biochemistry (2004) 43(39) 12539-48. PMID: 15449943 -- John J. Tanner Professor of Chemistry and Biochemistry University of Missouri-Columbia 125 Chemistry Building Columbia, MO 65211 Phone: 573-884-1280 Fax: 573-882-2754 Email: [EMAIL PROTECTED] http://www.chem.missouri.edu/TannerGroup/tanner.html From: Michael Jackson <[EMAIL PROTECTED]> Reply-To: <[EMAIL PROTECTED]> Date: Wed, 29 Oct 2008 10:29:22 -0700 To: <[email protected]> Subject: [ccp4bb] PEG degradation/properties lit source Hello, I would greatly appreciate anyone who would know of a basic literature source on the properties of PEG and particularly on PEG decomposition or degradation products. We see densities in our maps for ethanol molecules, but our condition for the crystals do not have added ethanol.
