why the buffer contains the EDTA and MnCL2 at the same time? - Help!!! (Feb/11/2007 )
sample buffer is 50mM Tris pH 7.5， 1mM EDTA，1mM DTT，2mM MnCl2 and 5% glycerol、elution buffer A is the same as sample buffer but no glycerol。I am wondering why the buffer contains the EDTA and MnCL2 at the same time? The buffer protocol is from many published paper. And another problem is EDTA is not campatible to Mg2+?
what do u mean by "contains the EDTA and MnCL2 at the same time"??!! 
EDTA is a chelator and its work is to chelate ions and hence preventing them from precipitating in solutions..
is this make a sense...or i misunderstand your Q??
EDTA-MnCl2 build a buffer system for free Mn2+
you can also create a buffer system with EDTA-MgCl2 for free Mg2+
Doesn't this have something to do with a slow release of Mg2+? I know a buffer (for culture of fungi) with both EDTA and Ca, and the EDTA in this buffer is for the slow release of Ca.
I do not really know about a slow release: may be you mean the release of Mn2+ (for a EDTA-MnCl2-buffer) from EGTA-Mn to medium after complexing free Mn2+ at another sink; that is the nature of a buffer: to maintain a constant level of, here, a certain cation (Mn2+);
another advice: one should calculate and provide the conc of FREE Mn2+ released from the EDTA-MnCl2 buffer; programs and online-calculators are around /f.i. Eqcal, Chelator etc)
Sorry, I indeed ment slow release of Mn2+. That was one of the questions right, why both EDTA and MnCl2?
so you mean why buffering free Mn2+ at all? higher conc of Mn2+ are toxic and counteract Mg2+-dependent processes whereas low level Mn2+ can substitute even Mg2+
caculating is believing: Try to determine the wished conc of free Mn2+ by putting in conc of EDTA and MnCl2 in, let´s say, Eqcal; see what happens if you set your EDTA conc at "0"