Deamination by the diazotization-deazotization method

Synopsis The diazotization-deazotization method for deaminating proteins in fixed tissue section, as originally described by Stoward (1963), has been investigated further with the following results. Blocking of arginine was confirmed by the Sakaguchi method and with anionic dyes. What appeared to be staining of lysine by anionic dyes was blocked but the dinitrofluorobenzene reaction was not. Blocking of histidine could not be demonstrated. Tyrosine was blocked to Millon's reagent but not to the coupled tetrazonium reaction. Staining of sulphydryl groups by Barrnett & Seligman's dihydroxydinaphthyldisulphide method was reduced but not obliterated. The colour of the reaction product between tryptophan residues and dimethylaminobenzaldehydenitrite was altered. Explanations for these findings are suggested.