I wouldn't use a pH of 9 when dealing with metal cations in solution.
By and large, metal hydroxides precipitate at alkaline pH.
HTH
Pr. Nadir T. Mrabet
Cellular & Molecular Biochemistry
INSERM U-954
Nancy University, School of Medicine
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Guenter Fritz wrote:
Ho,
interesting case.
Glycerol actually forms weak complexes with metal ions:
Journal of Inorganic Biochemistry,60 299-302 (1995) and some
references therein.
But to be true, I am surprised that glycerol at concentrations of
10-15% (?) as used in cryo conditions can compete with a metal ion
binding site in a protein. I remember I myself did titrations with
Zn2+ in the presence/absence of 5% glycerol and did not observe any
effect on the binding. There might be another effect (?) although I
have no idea what it might be.
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
