White H L, Wu J C
Biochem J. 1975 Feb;145(2):135-43. doi: 10.1042/bj1450135.
Kinetic and electrophoretic properties of catechol O-methyltransferases (EC 2.1.1.6) from brain and liver were studied. The enzyme of either rat or human tissues exhibited a single molecular form when subjected to electrophoresis at pH7.9. At pH9 a second, apparently oxidized, form was detected. Isoelectric-focusing experiments also indicated only one enzyme form, which was identical from extracts of brain and liver of each species (pI = 5.2 for rat, 5.5 for human). Similarities between brain and liver catechol O-methyltransferase of a given species were also demonstrated by kinetic parameters, meta/para ratios of products, and inhibitor potencies. Human catechol O-methyltransferase exhibited lower Km values than did the rat enzyme for S-adenosyl-L-methionine, dopamine and dihydroxybenzoic acid. Adrenochrome inhibited both rat and human enzyme. It was concluded (1) that only a single enzyme form could be demonstrated in the physiological pH region; (2) that catechol O-methyltransferase of brain could not be distinguished from the liver enzyme of the same species; and (3) that species differences exist between the enzymes of rat and human tissues.
对来自脑和肝脏的儿茶酚-O-甲基转移酶（EC 2.1.1.6）的动力学和电泳性质进行了研究。当在pH7.9条件下进行电泳时，大鼠或人体组织的该酶均呈现单一分子形式。在pH9时，检测到第二种明显氧化的形式。等电聚焦实验也仅表明有一种酶形式，且每个物种脑和肝脏提取物中的酶形式相同（大鼠的pI = 5.2，人类的pI = 5.5）。给定物种脑和肝脏的儿茶酚-O-甲基转移酶之间的相似性还通过动力学参数、产物的间位/对位比例以及抑制剂效力得以证明。对于S-腺苷-L-甲硫氨酸、多巴胺和二羟基苯甲酸，人类儿茶酚-O-甲基转移酶的Km值低于大鼠酶。肾上腺色素对大鼠和人类的酶均有抑制作用。得出的结论是：（1）在生理pH区域只能证明有一种单一的酶形式；（2）同一物种脑的儿茶酚-O-甲基转移酶与肝脏的酶无法区分；（3）大鼠和人体组织的酶之间存在物种差异。
