Abstract
1. With the finding of the photosensitivity of protein-bound diazotyrosin, a reproducible and sensitive reaction for tyrosine and certain other phenolic compounds in tissue sections based on diazotization and coupling is presented.
2. The specificity of the diazotization-coupling reaction for protein-bound tyrosine among the amino acids is established and the histochemical localization of tyrosine-containing protein in numerous tissues is described.
3. A modification producing a formazan product is presented, which, however, is too insensitive for exacting histochemical use. A modification producing o,o’-dihydroxyazo compounds, which give excellent histochemical localization and are capable of metal chelation, is described, and the possible use of the uranyl chelate for the demonstration of tyrosine by electron microscopy is suggested.