MONOAMINE-OXIDASE ACTIVITIES IN CATFISH (PARASILURUS-ASOTUS) TISSUES

The substrate- and inhibitor-related characteristics of monoamine oxid ase (MAO) were studied for catfish brain and liver. The kinetic consta nts for MAO in both tissues were determined using 5-hydroxytryptamine (5-HT), tyramine and beta-phenylethylamine (PEA) as substrates. For bo th tissues, the V-max values were highest with 5-HT and lowest with PE A. The K-m value for the brain was highest with 5-HT, followed by tyra mine and PEA; but for the liver its value was highest with PEA, follow ed by 5-HT and tyramine, although all values were in the same order of magnitude. The inhibition of MAO by clorgyline and deprenyl by use of 5-HT, tyramine and PEA as substrates showed that the MAO-A inhibitor clorgyline was more effective than the MAO-B inhibitor deprenyl for bo th catfish tissues; a single form was present since inhibition by clor gyline or deprenyl with 1000 mu M PEA showed single phase sigmoid curv es. It is concluded that catfish brain and liver contain a single form of MAO, relatively similar to mammalian MAO-A.