On the active site of diamine oxidase: Kinetic studies

Kinetic data are presented describing interaction of pig kidney diamine oxidase with different substrates and inhibitors. Vmax and Km values have been measured at pH 7.4 for various amino compounds. Km values, which have been obtained at pH 6.3, 7.4, and 8.5 for cadaverine, histamiue, and butylamine, range from 10−3 to 10−5m. Data are also presented on the inhibition of pig kidney diamine oxidase by high substrate concentrations. Diamines show such type of inhibitory behaviour, whereas with monoamines no inhibition appears even at concentrations as high as 1 m. The inhibition due to substrate is completely reversible. K′s values for cadaverine and histamine at different pH values have been calculated. The enzyme is competitively inhibited by aromatic diamines such as o- and m-phenylenediamine. These results are discussed in terms of an active site containing binding sites for the amino groups to be oxidized, for the aliphatic hydrocarbon chain of substrates, and an anionic binding site for positively charged groups at the opposite end of the molecule.