Aldehyde dehydrogenase and monoamine oxidase in rat liver mitochondria

Monoamine oxidase (EC 1.4.3.4) and aldehyde dehydrogenase (EC 1.2.1.3) activities were compared in the liver mitochondria of male and female rats. Monoamine oxidase activity using benzylamine as a substrate was significantly higher in males as compared with females: 1.45 versus 0.74 mumols/mg mitochondrial protein/hr, respectively. Monoamine oxidase activity using tyramine as a substrate and aldehyde dehydrogenase activity were the same in males and females. Monoamine oxidase-tyramine and aldehyde dehydrogenase activities did not vary with the different phases of the estrous cycle in the female but the activity of monoamine oxidase-benzylamine did; rats in the proestrous phase had the highest activity and those in the estrous phase had the lowest.