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Updated: Jul 24, 2026

Modification and Functionalization of the Guanidine Group by Tailor-made Precursors
Published on: April 27, 2017
Histochemistry of guanylate cyclase activity
S Mehdizadeh1, A O'Farrell, L Bitensky
1Department of Medicine, Charing Cross and Westminster Medical School, London, United Kingdom.
Abstract:
Guanylate cyclase liberates pyrophosphate from guanosine triphosphate (GTP). In studies published previously, this phosphate is trapped by lead ions even though it is known that free lead ions inactivate a considerable proportion of this enzymatic activity. To overcome the damaging effects of fixation, this study used fresh cryostat sections stabilized with a sufficient concentration of a collagen-derived polypeptide to ensure no measurable loss of guanylate cyclase activity. To avoid the damaging influence of free lead ions, we used a hidden metal capture reagent, i.e., a complex of lead ammonium citrate/acetate that does not react with GTP but which rapidly forms a precipitate with the pyrophosphate liberated by the enzyme. The lead precipitate is then converted into the colored sulfide which is measured in individual cells by microdensitometry. This system was used to measure guanylate cyclase activity in individual cells in unfixed sections of rat liver.
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