Polyamine oxidase (PAO) activity was found in the brain, intestine, kidney and liver of the siluroid catfish using N1-acetylspermine as substrate. It was highest in the intestine and lowest in the brain. 2. Substrate specificity of the enzyme was tested in the intestine and liver and the highest activity was found with N1-acetylspermine, followed by N1-acetylspermidine and N1,N12-diacetylspermine. 3. The apparent Km values for N1-acetylspermine were 19.6 and 46.9 microM for the intestine and liver, respectively. 4. These results suggest the presence of a system of polyamine reutilization after their acetylation in fishes.
