Re: nuclc acid fix (TCA+); also Barbi

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From:"J. A. Kiernan" <jkiernan@julian.uwo.ca>
To:Histonet <histonet@pathology.swmed.edu>
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A lot of questions --->  A long answer. 
Delete now if you aren't interested.

On Mon, 15 May 2000, Mike King wrote:
> > non-formaldehyde fixatives for better preservation of DNA and RNA
> and John Kiernan replied:
> ...In traditional histochemistry the best fixatives for DNA and RNA...
>  Are you ... aware of any attempts to incorporate into fixatives reagents
> such as trichloracetic acid, used to precipitate DNA in biochemical
> preparations?  Or RNAse inhibitors?

Reply:

  RNase inhibitors: Diethylpyrocarbonate has been used, but (I think)
  for the wrong reasons. I'll check and report if anything turns up.

  Trichloroacetic acid (TCA) is a coagulant fixative of proteins.
  According to M. Gabe's big book "Histological Techniques" (1975)
  it preserves much more delicate structure than one would expect
  when used alone. In real practice TCA is used only as a component 
  of Heidenhain's SUSA. This is one of the best fixatives for light 
  microscopy, but is currently _fixator_non_grata_ on account of
  its containing mercuric chloride and other poisonous chemicals,
  including TCA. The TCA in SUSA may help in precipitating DNA, but
  the mixture also contains enough acetic acid to do this quite
  adequately. Much higher concentrations of TCA _extract_ nucleic
  acids from fixed tissues. TCA and also perchloric acid are still 
  used histochemically for this purpose, as are DNase and RNase.

  Please be aware that it's not "Susa's fixative." A Susa did not 
  invent it, and neither did Heidenhain name this excellent fixative 
  after his favourite bird. SUSA is an acronym for Sublimat-Saure 
  (with a few umlauts that can't be sent by email), which roughly 
  translates to mercuric chloride with acids.  Barbituric acid,
  barbiturates and all the other "barbi-" compounds commemorate
  "a lady named Barbara" revered and perpetuated by a particularly
  perspicacious chemist of the 1890s who recognized an unconventional 
  "acid" structure.  Can anyone remember the clever chemist's name? 

  Eponyms are fun.

 John A. Kiernan,
 Department of Anatomy & Cell Biology,
 The University of Western Ontario,
 LONDON,  Canada  N6A 5C1
 




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