Abstract
Monoamine oxidase (MAO) in homogenate and mitochondria from frog liver and brain were studied using a radiometric method of Wurtman and Axelrod with 14C-tyramine, 14C-β-phenylethylamine (PEA), 14C-5-hydroxytryptamine (5-HT) and 14C-benzylamine as substrates. The highest activity in frog liver was obtained in mitochondrial fraction which is the same as in many other organs of mammalian. MAO activities in frog liver and brain with tyramine as a substrate increased with increase in the enzyme volume between 5μl to 25 μl and with increase in the incubation time between 5 min to 25 min in lineal manner. The optimum pH of the MAO activities were obtained at pH 7.4 in liver and brain preparations. Tris-HCl caused inhibition on MAO activities in liver and brain about 50%. MAO in frog brain and liver homogenate and mitochondria were stable for 28 days when they were kept in frozen. MAO activities with tyramine and PEA were higher than those with 5-HT and benzylamine in brain and liver homogenate and mitochondria. From the results of the effects of incubation and preincubation temperature on MAO in liver and brain homogenates with various substrates, MAO in liver and brain were thought to be consisted of two groups of enzyme. One was unstable on heat treatment and deaminated tyramine and PEA, and the other was stable on it and deaminated 5-HT. From these results, in frog liver and brain, there may be two different types of mitochondrial MAO which were resemble to type A and type B MAO in many organs of mammalian.
