I am working with a metalloprotein that binds cobalt and iron. I was surprised that the solved structures showed the crystals cryoprotected with glycerol are metal free while crystals cryoprotected with ethylene glycol had the metals present. Both cryoprotectant solutions contained metal in the 10 mM range and are buffered at pH 9. I assume glycerol must be a weak chelator otherwise it wouldn't be so ubiquitous in protein biochemistry. Has anyone else experienced this before with glycerol?
Ho UC Berkeley
