Abstract

1. Catechol-O-methyltransferase (COMT) methylates both endogenous and exogenous catechol compounds to inactive and safe metabolites.

2. We first optimized conditions for a convenient and sensitive continuous fluorescence-based 6-O-methylation assay of esculetin, which we used for investigating the COMT activity in human, mouse, rat, dog, rabbit, and sheep liver cytosols and microsomes and in ten different rat tissues. Furthermore, we compared the inhibition potencies and mechanisms of two clinically used COMT inhibitors, entacapone and tolcapone, in these species.

3. In most tissues, the COMT activity was at least three times higher in cytosol than in microsomes. In the rat, the highest COMT activity was found in the liver, followed by kidney, ileum, thymus, spleen, lung, pancreas, heart, brain, and finally, skeletal muscle. Entacapone and tolcapone were characterized as highly potent mixed type tight-binding inhibitors. The competitive inhibition type dominated over the uncompetitive inhibition with entacapone, whereas uncompetitive inhibition dominated with tolcapone.

4. Rats, dogs, pigs, and sheep are high COMT activity species, in contrast to humans, mice, and rabbits; COMT activity is highest in the liver. Both entacapone and tolcapone are potent COMT inhibitors, but their inhibition mechanisms differ.

摘要

1. 儿茶酚-O-甲基转移酶（COMT）将内源性和外源性邻苯二酚化合物甲基化为无活性和安全的代谢产物。

2. 我们首先优化了一种简便，灵敏的基于七叶草素的连续荧光基6- O-甲基化测定的条件，我们将其用于研究人，小鼠，大鼠，狗，兔和绵羊的肝细胞溶胶和微粒体中的COMT活性，并研究了十种不同的大鼠组织。此外，我们比较了在这些物种中两种临床使用的COMT抑制剂entacapone和tolcapone的抑制能力和机理。

3. 在大多数组织中，胞浆中的COMT活性至少是微粒体的三倍。在大鼠中，肝脏的COMT活性最高，其次是肾脏，回肠，胸腺，脾脏，肺，胰腺，心脏，大脑，最后是骨骼肌。恩他卡朋和托卡朋被认为是高效的混合型紧密结合抑制剂。竞争性抑制类型优于用恩他卡朋的非竞争性抑制，而竞争性抑制则以托卡朋为主导。

4. 与人，小鼠和兔子相反，大鼠，狗，猪和绵羊是高COMT活性物种。肝中的COMT活性最高。entacapone和tolcapone都是有效的COMT抑制剂，但它们的抑制机制不同。