A homogeneous preparation of pig kidney diamine oxidase was obtained by polyacrylamide gel electrophoresis and immunodiffusion. Its molecular weight was estimated as 170,000 by Sephadex G-200 column chromatography and as 220,000 by SDS-polyacrylamide gelelectrophoresis. After mercaptoethanol cleavage of disulfide bonding, the molecular weight of the subunit was 130,000. 2. Little contamination was observed in the preparation of human placenta by SDS-polyacrylamide gel electrophoresis and immunoelectrophoresis and the molecular weight was calculated as 30008000 and 280,000 by the extrapolation from the calibration curve of Sephadex G-200 column chromatography and SDS-polyacrylamide gel electrophoresis, respectively. The subunit was 170,000. 3. By immunodiffusion, immunoelectrophoresis and inhibition test of the enzyme activity using a heterologous antiserum, a good cross-reactivity was observed between the anti-human diamine oxidase serum and pig diamine oxidase. 4. The activities of the two enzymes were not almost inhibited by homologous and heterologous antisera.
