Purification and characterization of diamine oxidase (histaminase) from rat small intestine

Diamine oxidase (DAO) was purified to homogeneity from rat small intestine, and its biochemical and immunochemical properties were studied. DAO was suggested to be a dimer of a 92 kDa subunit, and its isoelectric point was found to be 6.0. Histamine, putrescine, N tau-methylhistamine, and cadaverine were good substrates, with Km values ranging from 9.4 to 16.0 microM. Spermine and spermidine were not substrates. Both an immunoprecipitation study and Ouchterlony's double diffusion test involving antiserum against the purified DAO showed that the immunological properties of the DAOs from rat small intestine, thymus, and placenta were identical. Among small intestinal DAOs from different species, this antibody reacted to the guinea pig enzyme as strongly as to the rat enzyme, but the reaction was much weaker to the mouse enzyme than to the rat enzyme. The DAOs from rabbit and dog small intestine, pig kidney, and human placenta showed no reactivity toward this antibody.