Abstract
When 2-hydroxylated oestrogens are incubated with the 150,000 g supernatant of rat brain in the presence of S-adenosylmethionine, the isomeric 2- and 3- monomethyl ethers are formed. The enzymic methylation of 2-hydroxyoestradiol-17β and 2-hydroxy-17α-ethinyloestradiol-17β in brain tissue is catalysed by a S-adenosylmethionine: catechol O-methyltransferase (EC 2.1.1.6) which exhibits similar kinetics as the catechol O-methyltransferase of human liver. The Km values were 19 μM for 2-hydroxyoestradiol-17β and 36 μM for 2-hydroxy-17α-ethinyloestradiol-17β; the Km values for catechol amines were about 10 times higher and amounted to 320 μM for adrenaline, 270 μM for noradrenaline and 240 μM for dopamine. These findings indicated that the methylation of catechol amines by the brain catechol O-methyltransferase may be inhibited by catechol oestrogens. Accordingly, the effect of 2-hydroxyoestradiol-17β and 2-hydroxy-17α-ethinyloestra iol-17β on the methylation of adrenaline, noradrenaline and dopamine has been studied,
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