Zn precipitation of proteins

gerald hs0lbe at orac.sund.ac.uk
Thu Jan 15 12:43:42 EST 1998

Pete wrote:
> Does anyone know any specific protein complexes that are precipitated
> from tissue homogenates by the addition of 1 mM Zn chloride.
> I get a huge precipitate when I add more than 0.1 mM Zn chloride that
> seems to contain specific proteins. If I only had a clue what these
> proteins could be...
> |)    |/
> |etri |\ursula

Well I guess the exact identity could depend upon the tissue that sample
was derived from.
However, since one of the most common, and strongest, Zn2+ coordinating
amino acid residues is His, followed by Glu, what ever they are, they
are likely to contain significant amounts of these amino acids with an
appropriate geometry for  Zn2+ coordination.

There are a number of Zn2+ proteins in tissue, Zn2+ being a common metal
centre in metalloenzymes.  It is also, obviously from their name,
directly connected with the DNA associated proteins - zinc-finger
proteins, which would clearly occur in almost what ever tissue you were

A large No of proteins, say albumins, can also exhibit non-specific
binding of metal ions such as Cu2+ and probably Zn2+ as well.  pH can
enhance this effect, ie. higher pH leads to more metal coordination. 
However your metal concentration  [0.1mM] unless your working at pH>8
would not be expected to produce the dramatic effect you describe
through these nonspecific associations.

So the best idea on how to identify them would be isolate the ppt
protein,  resuspended them in an EDTA buffer, dialyse out the Zn2+,
seperate them out on the SDS-PAGE and get sequencing.

Dr Len Bell,
University of Liverpool.
email: lgbell at liv.ac.uk

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