Studies in fluorescence histochemistry

Summary Pretreatment of sections of fixed tissue with selective blocking reagents for indigenous thiol groups did not, it was found, impair the fluorescence subsequently obtainable with the acetic anhydridesalicylhydrazide-zinc technique (Stoward and Burns, 1967) for localizing C-terminal carboxyl groups of proteins. This suggests that thiol and S-acetyl groups do not participate in the complex reactions involved in the method. In further support of this suggestion it was found that artificially introduced thiol groups also do not take part.Sites containing either, glycogen or neutral periodate-reactive mucosubstances did not fluoresce in sections subjected to the technique. This indicates that O-acetyl groups, although probably formed, are not involved in the reactions giving rise to the fluorescence reaction in proteins.