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DOI: 10.1055/s-2007-1004856
© Georg Thieme Verlag, Stuttgart · New York
Monoamine Oxidase A Mediates Iodotyrosine Formation Induced by Monoamines in Bovine Thyroid Particulate Fraction
Publication History
1989
1989
Publication Date:
14 March 2008 (online)
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Summary
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 β-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 was for 5-HT and the highest for tyramine. The amount of iodine incorporated to tyrosine was not equivalent to the H2O2 generated by the monoamines nor to that exogenously added.
Our results indicate that in bovine thyroid tissue mainly the A form of MAO is involved in the monoamine metabolism.
Key words
Iodotyrosine Formation - Thyroid Monoamine Oxidase (MAO) - MAO A-Clorgyline - Deprenyl - Monoamines