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人体内的大部分外来化合物由尿排泄。肾脏能排泄水溶性物质,但排泄亲脂物的能力有限。肝细胞内质网中有一体系,能使氧分子掺入各种非极性物质,因而使其变为极性物质。这一体系的中心成分是细胞色素 P-450,为血红素蛋白。它是一组同功酶,与底物有特异性竞争作用。其主要功能是活化分子氧,使一个氧原子掺入底物,另一个还原生成水分子:
Most of the body’s foreign compounds are excreted by the urine. The kidneys can excrete water-soluble substances, but the ability to excrete lipophilic substances is limited. There is a system in the endoplasmic reticulum of liver cells, which enables oxygen molecules to be incorporated into various non-polar substances, thus making them polar substances. The central component of this system is cytochrome P-450, a heme protein. It is a group of isoenzymes that specifically compete with substrates. Its main function is to activate molecular oxygen so that one oxygen atom is incorporated into the substrate and the other is reduced to form water molecules: