Light microscopic visualization of diamine oxidase using a cerium method

Diamine oxidase (DAOX) can be localized in the light microscope using immunohistochemistry, but a reliable procedure for detecting the activity of the enzyme does not exist. A method was thus developed in which cerium ions trap H2O2, generated by DAOX, and a diaminobenzidine-H2O2-Co sequence serves for the visualization of the primary reaction product cerium perhydroxide. With this method and diamine substrates cadaverine or putrescine, or polyamine substrates spermidine or spermine as substrates, DAOX was localized species-independently but substrate-dependently in the basolateral cytoplasm and/or plasma membrane of small intestinal enterocytes of rats, mice and gerbils. Less, or even no, final reaction product was seen in these cells of guinea-pigs and marmosets. Colonic enterocytes were positive for DAOX solely in gerbils. Furthermore, species-dependent diamine oxidase was present in special cells of the mouse and guinea-pig kidney, immune organs and liver of rats and gerbils, marmoset placenta and in decidual cells of the human, rat and mouse placenta.