On Thu, 2 Dec 1999, Corazon Bucana wrote:

> Just out of curiousity, is there a peroxidase substrate  for
> immunohistochemistry that forms an insoluble precipitate and at the same
> time is also fluorescent?

  Yes. The procedure known as TAT (tyramide amplification
  technique) or CARD (catalysed reporter deposition) is a
  sensitive method for peroxidase. It generates a fluorescent
  product that is covalently bound to the tissue at sites
  of enzymatic activity. The chromogen is a compound made by
  linking tyramine to a fluorochrome. In the presence of
  peroxidase and its substrate, hydrogen peroxide, the
  tyramine half of the chromogen molecule is oxidized to
  a highly reactive free radical, which immediately reacts
  with and binds to protein (probably mainly to tyrosine)
  in the tissue. Simple methods for synthesizing fluorescently
  labelled tyramides are described by Hopman,AHN et al (1998)
  in J Histochem Cytochem 46:771-777.

  I haven't tried this myself, but the published pictures
  are impressive. It is used more for in situ hybridization
  than for imunohistochemistry, but is suitable for any
  technique in which peroxidase activity needs to be
  localized.

 John A. Kiernan,
 Department of Anatomy & Cell Biology,
 The University of Western Ontario,
 LONDON,  Canada  N6A 5C1
   E-mail: kiernan@uwo.ca