Negative stain

[Philip Koeck]

The problem of positive staining is certainly important at higher
resolution but I don't understand the first part of Carmen's message.

In regular cryo a slightly denser specimen is embedded in slightly less
dense
homogenous vitrified water, whereas in cryo negative stain a slightly less
dense specimen is embedded in a denser, (hopefully) equally homogenous
stain solution.
Why should one only see outlines in the second case?
To me it seems that the only thing that has changed is a constant background
value in the images.

Philip

----- Original Message -----
From: "Carmen A. Mannella" <cam14 at health.state.ny.us>
To: <3DEM at SDSC.EDU>
Sent: Saturday, September 21, 2002 4:16 AM
Subject: Negative stain


> If the objective is to image the macromolecular density in a specimen,
> negative stain (cryo or otherwise) is not the way to go.  With it, you
> image the stain not the protein, nucleic acid, lipid, etc.  If you want
> outlines of the specimen, it is very useful, with the proviso that
> different metal salts give varying degrees of positive staining of select
> features, which can complicate interpretation of the object, especially at
> high resolution (below 2 nm or so).
>
> Carmen Mannella


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