RE: Note on Diastase!
To respond to your question below: Histology is, at best, a crude, yet microscopic observation of disease effects at the cellular level. Thus we are observing biochemical effects, but only reporting what we see at the cellular level. Our most common use of this procedure (PASD) is in liver biopsies in an attempt to exclude or diagnosis alpha-1-antitrypsin deficiency.
The alpha-1-antitrypsin globules accumulate in this disease within the hepatocytes. They are both PAS positive and diastase resistant. Thus, we use the diastase to get rid of hepatocyte glycogen staining so that we can evaluate the liver for these globules. As mentioned, this is only a crude indicator of possible AAT deficiency. Other hepatic changes are evaluated with routine stains and more sensitive and specific immunohistochemistry is used when needed. Additionally, the final diagnosis rests with the clinician who correlates all the pathologic findings with clinical, serologic, genetic, etc. info to make this diagnosis.
Thus, though your point is valid and well taken, this is a very small part of the puzzle and we do not usually get excited about enzyme specificity.
From: Monson, Frederick C. [mailto:firstname.lastname@example.org]
Sent: Monday, January 21, 2002 11:19 AM
Subject: Note on Diastase!
What follows is my own opinion, of course, but I think it is always correct
to think about the matter of what one is doing every once in a while.
1. I have searched for what I wanted, and I found it: A
PAS/Diastase-control method that mentions what happens if one over-shoots
with the enzyme. (URL:
http://medlib.med.utah.edu/WebPath/HISTHTML/MANUALS/PASD.PDF) [Sorry about
2. I have failed to find diastase specified as a PURE entity in any
source, and most of the references in Google, at least, come from the
3. When I read the recommendation for using saliva, 25+ years ago,
I was immediately aware, from my training in biochemistry, that while the
demonstration of the effect of salivary amylase on bread while masticated
for 10 minutes was the foundation of an important freshman biology lab,
there were OTHER, powerful enzymes present in that solution.
4. alpha-amylase (URL:
http://www.worthington-biochem.com/manual/A/AA.html) happened to be
available from one of the biochemists nearby, and I tried that (as had
others! - reference lost???). Even then one could get "CRUDE" and/or
"PURIFIED" amylases from Sigma and/or Worthington.
5. THE POINT: While the PAS is considered to be specific for
vic-glycols (the oxidation of Malaprade), primarily in glycogen (or starch),
the control has always been performed with rather casual attention to what
might correctly be called in this case, "collateral damage" to the
6. While I have used the PAS without the expensive control, because
I haven't used it for anything more significant than general histochemistry,
I have often wondered about the conclusions we all draw when we use this
method. (URL: http://medocs.ucdavis.edu/hph/400/GIintro/sld022.htm)
QUESTION: Even knowing that "diastase" is perhaps better than saliva, how
do you folks in pathology treat the issue of enzymatic specificity in this
case, or others?
Frederick C. Monson, PhD
The best research
Center for Advanced Scientific Imaging
occurs before work
West Chester University
at the bench.
West Chester, Pennsylvania, USA, 19383
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