[Monamine oxidase (MAO)].

Serum monoamine oxidase (MAO) was separated electrophoretically into three bands. These bands were termed as Fraction I, II and III in that order from anode to cathode. Elevation of serum MAO activity in Fraction I was observed in patients with organ fibrosis particularly in liver cirrhosis and acromegaly. On the other hand, elevation of MAO activity in Fraction II was observed in patients with massive hepatic necrosis. MAO activities partially purified from aortic vessel and from rat liver mitochondria had electrophoretically in the same position as Fraction I and II respectively. Both of Fraction I and aortic extract were inhibited by aminoacetonitrile but not by pargyline. On the contrary, both of Fraction II and mitochondria were inhibited by pargyline but not by aminoacetonitrile. These findings suggested that the elevation of serum MAO in patients with organ fibrosis correlates with the enhancement of connective tissue metabolism and the increment of serum MAO in fulminant hepatitis correlates with the breakaway of MAO from damaged liver mitochondria.