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The title reaction—so convincing on paper—succeeds only in the presence of the right catalysts. Combinations of a weak Lewis acid and a Lewis base, e.g. diisobutylaluminum hydride/triphenylphosphane, accelerate formation of carbonate from carbamic esters and alcohols to such an extent that the competing elimination of isocyanic acid is suppressed.

When 2-hydroxyoestradiol-178 was incubated in the presence of S-adenosylmethionine With a 380-fold purified catechol 0-methyltransferase from human liver, 2-methoxyoestradiol-178 and 2-hydroxyoestradiol-178 3-methyl ether were identified as the only metabolites. No dimethylation, transmethylation or demethylation was observed.The purified enzyme was active only in the presence of cysteine and divalent cations; magnesium was found to be the most effective cation. The temperature optimum for the methylation of 2-hydroxyoestradiol-l7,9 was 42 "C ; the activation energy amounted to 20.9 kcal/mol. The enzyme activity had two pH optima; the pH optimum between 6.8 and 8.4 was due to maximal formation of 2-methoxyoestradiol-l7~, whereas the pH optimum a t 9.2 was due to the formation of both the 2-and 3-monomethyl ether.The formation of the two isomeric monomethyl ethers increased to a maximum a t a substrate concentration of 50 pM ( K , value 14 pM) and then decreased with an inflection point between 75 and 100 pM (Ki value under standard assay conditions 95 pM). Whereas both monomethyl ethers were formed at the same rate up to 50 pM substrate concentration, the decrease of formation of 2-hydroxyoestradiol-17fi 3-methyl ether was more pronounced than that of 2-methoxyoestradiol-178. Both substrate inhibition and the ratio of methylation depended on the concentrations of X-adenosylmethionine and MgC1,. Product inhibition was also demonstrated with Ki values of 24 pM for 2-methoxyoestradiol-178, 80 yM for 2-hydroxyoestradiol-l7/? 3-methyl ether and 39 [*M for X-adenosylhomocysteine. I n contrast, increasing amounts of S-adenosylmethionine did not produce inhibition or changes of the ratio of methylation ( K , value 8.5 pM).Catechol 0-methyltransferases are important enzymes in the metabolism of catechols and have been found in animal and human tissues (cf. [1-31); they catalyse the transfer of the methyl group of S-adenosyl-L-methionine to compounds with a catechol structure. The kinetic properties of these enzymes have been the subject of many studies (cf. [1,[3][4][5][6][7][8][9][10]). Most of the attempts to purify and characterise the catechol 0-methyltransferases have been limited to rat liver ; one exception is a recent report concerning human placenta [3].I n view of the importance of the catechol 0-methyltransferase in the intermediary metabolism of catechol amines as well as of oestrogens in man, experiments were undertaken to isolate the enzyme from human liver [ll]. A catechol O-methyltransEnzyme. Catechol 0-methyltransferase or S-adenosylmethionine : catechol 0-methyltransferase (EC 2.1.1.6).Trivial Names. 2-Hydroxyoestradiol-l7/3, 1,3,5(10)-oestratriene-2,3,17,9-triol; 2-methoxy-oestradiol-17j3,2-methoxy-1,3,5(10)-oestratriene-3,17j3-diol; 2-hydroxy-oestradiol-178 3-methyl ether, 3-methoxy-1,3,5(10)-oestratriene-2,l7j3-diol.ferase was purified 380-fold from human liver and in the present paper the kinetic properties of this enzyme are described. i.e. 1,3,5( lO)-oestratriene-2,3,17j3-triol, was generously do...

Radioactive oestradiol was incubated with homogenates of hypothalamus, pituitary and liver and slices of cortex, hippocampus, hypothalamus, pituitary and liver of ovariectomized rats. 2-and 4-substituted oestrogens were the main metabolites in the brain and were found in the same proportions.In the liver only the 2-substituted oestrogens were the main metabolites, while the 4-substituted ones were of minor quantitative importance. On the basis of wet weight the 2-hydroxylating capacity of the liver was approximately 50 fold greater than that of the brain and the 4-hydroxylating capacity about the same as that of the brain. Only slight differences in the 2-and 4-hydroxylating capacity of various brain areas were observed, although apparently the hypothalamus and the pituitary were more active in the formation of catecholoestrogens than the cortex and the hippocampus.The importance of oestradiol in the control of the hypothalamic-pituitary function is well established (Vande Wiele et al. 1970; Young 8c Jaffe 1976).A recent report concerning the participation of catecholamines in this process (Kamberi 1974) and our findings dealing with the competitive interaction of catecholamines and catecholoestrogens via the catechol O-methyltransferase