Abstract
Some properties of monoamine oxidase (MAO) in carp heart homogenate were studied using the radioisometric method with14C-tyramine, 14C-5-hydroxytryptamine (5-HT) and14C-β-phenylethylamine (PEA) as substrates. The Michaelis-Menten kinetic constants (Km values) of the enzyme for tyramine, 5-HT and PEA were determined from Lineweaver-Burk plots. MAO activities in carp heart homogenate with tyramine, 5-HT and PEA as substrates increased with increase in the enzyme volume up to 30μl at a protein content of 4.3 mg/ml and with increase in the incubation time up to 30 min in linear manner. The optimum pH and temperature in this enzyme reaction were observed at pH 8.0 and 37.0°C with tyramine, 5-HT and PEA as substrates. MAO in carp heart homogenate was stable for 56 days when they were stored at -20°C until use for assay. The thermostabilities of MAO in three subcellular fractions of carp heart were examined with tyramine, 5-HT and PEA as substrates and found to be more thermostable than those of carp liver. Among these fractions, the enzyme in nuclear fraction was the most thermostable. In inhibition studies using clorgyline, deprenyl and semicarbazide as inhibitors, it is clear that carp heart contains a small amount of clorgyline resistant amine oxidase (CRAG) activity.
