Studies on monoamine oxidase. (Report 44) . Effect of sodium cholate on mitochondrial MAO from rabbit liver
Aman, S.
Nihon Yakurigaku Zasshi. Folia Pharmacologica Japonica 73(4): 449-456
1977
ISSN/ISBN: 0015-5691 PMID: 20394 Document Number: 115117
MAO activity decreased with increase in the concentration of sodium cholate when either tyramine or benzylamine was used as substrate and this activity was inhibited completely with 50 mM sodium cholate. Sodium cholate had no effect on MAO activity in rabbit serum. The pH optimum and pS maximum for tyramine were not changed when 10mM sodium cholate was added, while when benzylamine served as substrate inhibition with an excess of the substrate concentration occurred. Addition of 50 mM sodium cholate caused a complete inhibition of MAO activities with tyramine and benzylamine as substrates before dialysis and 45% and 75% after dialysis, respectively. Sodium cholate acted as an uncompetitive inhibitor for tyramine and benzylamine oxidation. After addition of various concentrations of sodium cholate to the mitochondria, the mixtures were centrifuged and MAO activities were measured in the supernatant and precipitate fractions. With increase in the concentration of sodium cholate, MAO activities in the supernatant increased and those in he precipitate decreased. When 50 mM sodium cholate was added, 50% of the activities were found in each fraction with tyramine as substrate, while when benzylamine was used as substrate, a 35% activity in the supernatant and a 65% activity in the precipitate fractions were noted. Substrate specificities for MAO activity in the supernatant and precipitate treated with 50 mM sodium cholate were quite similar to specificities in the mitochondria. When 2.5 mM sodium cholate was used to treat the mitochondria, MAO activities in the precipitate with serotonin and tryptamine as substrates were increased to over control values.