Rat thyroid monoamine oxidase (MAO) is regulated by thyrotrophin: evidence that the main form of the enzyme (MAO-A) is not directly involved in iodide organification

ANA MARIA DE LOS A. CABANILLAS; MASINI ANA,; COLEONI ALDO,

BIOSCIENTIFICA LTD

Año: 1991 vol. 131 p. 25 - 25

p>The characteristics and regulation of monoamine oxidase (MAO) were studied in rat thyroid tissue. A measured Michaelis constant (Km) value of 102 µmol/l was similar to the Km values found in other tissues. Maximal velocity (Vmax) was 1·028 nmol/mg protein per min. It is known that MAO is present as two isoenzymes, A and B, which are sensitive to clorgyline and deprenyl respectively. The in-vitro effect of graded concentrations of these selective MAO inhibitors was used to estimate the relative proportion of A and B isoenzymes. Clorgyline strongly decreased thyroid MAO activity at concentrations as low as 1 pmol/l while the effect of deprenyl was observed only at concentrations higher than 10 µmol/l. These results indicated that MAO-A is the main form of the enzyme in the rat thy