Raxworthy M J, Gulliver P A, Hughes P J
Naunyn Schmiedebergs Arch Pharmacol. 1982 Aug;320(2):182-8. doi: 10.1007/BF00506319.
Catechol-O-methyltransferase (COMT) activity on the extracellular face of the plasma membrane of isolated rat hepatocytes was assayed, and 4.3% of total COMT activity was located there in cells which satisfied our criteria of viability. However, since 1.2% of the cells' lactate dehydrogenase activity was also apparently extracellular, and this proportion increased to 3.4% under the conditions of the COMT assay the amounts of extracellular COMT may be even less. COMT in rat liver microsomes and plasma membranes represent 2.3% and 0.08% of total rat liver COMT respectively. This implies an insignificant role for plasma membrane COMT although reported altered kinetic behaviour could elevate microsomal COMT to a supporting role in the regulation of catecholamine concentration in the circulation. Since by far the largest fraction of COMT is located intracellularly in the soluble cell fraction, the physiological functions of COMT seem to be dependent on the passage of substrates through the cell membrane for their presentation to the enzyme.
对分离出的大鼠肝细胞质膜外表面的儿茶酚-O-甲基转移酶（COMT）活性进行了测定，在符合我们生存能力标准的细胞中，4.3%的总COMT活性位于质膜外表面。然而，由于1.2%的细胞乳酸脱氢酶活性也明显位于细胞外，并且在COMT测定条件下这一比例增加到3.4%，因此细胞外COMT的量可能更少。大鼠肝脏微粒体和质膜中的COMT分别占大鼠肝脏总COMT的2.3%和0.08%。这意味着质膜COMT的作用微不足道，尽管有报道称其动力学行为发生改变可能会使微粒体COMT在调节循环中儿茶酚胺浓度方面起到辅助作用。由于到目前为止，COMT的最大部分位于细胞内的可溶性细胞组分中，COMT的生理功能似乎依赖于底物通过细胞膜传递以呈递给该酶。
