Well, I happen to lecture on this...
The bible is "Data for biochemical research", Dawson et al., Oxford
University Press.
Should be available in most biochemistry labs, if not in the library.
Cheers,
Nadir
--
Pr. Nadir T. Mrabet
Cellular & Molecular Biochemistry
INSERM U-724
Nancy University, School of Medicine
9, Avenue de la Foret de Haye, BP 184
54505 Vandoeuvre-les-Nancy Cedex
France
Phone: +33 (0)3.83.68.32.73
Fax: +33 (0)3.83.68.32.79
E-mail: [log in to unmask]
Jacob Keller wrote:
> Could those who responded with numbers for affinities of imidazole for
> metal ions please divulge their sources? It is not that I doubt their
> veracities, but it would be a nice reference to have on hand.
>
> For those wondering about why I was asking about imidazole's affinity
> for metal ions, I was wondering whether the presence of imidazole
> would affect a metal-ion-dependent reaction. With, for example, 200 mM
> imidazole and 10 mM Ca++ or Mg++, what would be the amount of free
> metal? This can of course be calculated from imidazole's binding
> constant for these ions, which is another reason I ask for the sources
> of the numbers quoted in a couple of the responses.
>
> Thanks for all of the helpful responses so far,
>
> Jacob Keller
>
>
> *******************************************
> Jacob Pearson Keller
> Northwestern University
> Medical Scientist Training Program
> Dallos Laboratory
> F. Searle 1-240
> 2240 Campus Drive
> Evanston IL 60208
> lab: 847.491.2438
> cel: 773.608.9185
> email: [log in to unmask]
> *******************************************
>
> ----- Original Message ----- From: "Nadir T. Mrabet"
> <[log in to unmask]>
> To: "Jacob Keller" <[log in to unmask]>
> Cc: <[log in to unmask]>
> Sent: Friday, July 18, 2008 8:55 AM
> Subject: Re: [ccp4bb] Imidazole's ability to chelate metal ions
>
>
>> Imidazole can indeed complex (monodentate) metal ions but not chelate
>> them (bidendate, at least).
>> However, the stability constant, K, of such complexes is rather low,
>> eg log K = 0.1 for Mg, 3.3 for Fe and 4.2 for Cu.
>> In comparison, metal chelates are formed with EDTA, for which log K =
>> 10.6 for Mg, 14.2 for Fe and 18.8 for Cu.
>> So the difference amounts to several orders of magnitude.
>>
>> It should also be pointed out that the competitive effect of
>> imidazole in IMAC does not involve binding to free metal ions,
>> but instead coordination to immobilized metal chelates, eg
>> Ni(II)-nitrilotriacetate (Ni-NTA, where NTA is the chelator).
>>
>> In any situation where one assays a protein whose activity and/or
>> stability and/or else is/are metal dependent, one should
>> rather use buffers (see below) that do not interfere (eg Good's
>> buffers).
>>
>> I suspect the imidazole in your case is either a buffer (pKa 7.0) or
>> else results from competitive elution from an IMAC column.
>> What should be done depends on your exact conditions.
>>
>> hth,
>>
>> Nadir
>>
>> --
>>
>> Pr. Nadir T. Mrabet
>> Cellular & Molecular Biochemistry
>> INSERM U-724
>> Nancy University, School of Medicine
>> 9, Avenue de la Foret de Haye, BP 184
>> 54505 Vandoeuvre-les-Nancy Cedex
>> France
>> Phone: +33 (0)3.83.68.32.73
>> Fax: +33 (0)3.83.68.32.79
>> E-mail: [log in to unmask]
>>
>>
>>
>> Jacob Keller wrote:
>>> Dear Crystallographers,
>>> Does anybody happen to know whether imidazole is able to chelate
>>> metal ions in solution? It seems reasonable that since it can
>>> compete for binding to IMAC resins, it should have some affinity for
>>> at least Ni++ and Co++, but what about metal ions like Ca++ and
>>> Mg++? I assume that the affinity is weak, but at the concentrations
>>> at which we are wont to use it in our elutions (~100-500 mM), does
>>> it not seem likely that other metal ions are being competed away
>>> from our proteins as well?
>>> Jacob Keller
>>> *******************************************
>>> Jacob Pearson Keller
>>> Northwestern University
>>> Medical Scientist Training Program
>>> Dallos Laboratory
>>> F. Searle 1-240
>>> 2240 Campus Drive
>>> Evanston IL 60208
>>> lab: 847.491.2438
>>> cel: 773.608.9185
>>> email: [log in to unmask] <mailto:[log in to unmask]>
>>> *******************************************
>>
>
>
|