Monoamine oxidase A mediates iodotyrosine formation induced by monoamines in bovine thyroid particulate fraction

MASINI-REPISO ANA M, CABANILLAS ANA M, ANDRADA MARTA C, COLEONI ALDO H

HORMONE AND METABOLIC RESEARCH

Georg Thieme Verlag Stuttgart-NewYork

Lugar: Stuttgart, Germany; Año: 1990 vol. 22 p. 80 - 80

0018-5043

font size="2"> Monoamines are able to increase the thyroid iodine organification in vitro. A predominance of the A form of monoamine oxidase (MAO) has been previously demonstrated to exist in bovine thyroid tissue. In the present study we have investigated the form of MAO that could be involved in the iodotyrosine formation induced by tyramine, 5-hydroxytryptamine (5-HT) and beta-phenylethylamine (PEA) in a bovine thyroid subcellular fraction. The relative capacity of these monoamines to generate H2O2 and to incorporate iodine into tyrosine has also been studied. The MAO A inhibitor clorgyline (10(-9) M) produced a strong inhibition on the iodotyrosine formation induced by tyramine, 5-HT and PEA. In contrast, only a slight reduction was observed with deprenyl as MAO B inhibitor. Among the three monoamines, tyramine produced the highest H2O2 generation and iodotyrosine formation. The lowest Km value obtained was for 5-HT and the highest for PEA. Regarding the Vmax, the lowest value