Glick J M, Ross S, Leboy P S
Nucleic Acids Res. 1975 Oct;2(10):1639-51. doi: 10.1093/nar/2.10.1639.
Three tRNA methyltransferases from rat liver have been fractionated and purified greater than 100-fold. These enzymes have been examined for their sensitivity to inhibition by S-adenosylhomocysteine (SAH). The methyltransferase which forms m2-guanine in the region between the dihydrouridine loop and the acceptor stem of tRNA (m2-guanine methyltransferase I) is least sensitive to SAH inhibition, with a Ki of 8 muM. The enzyme responsible for forming m2-guanine between the dihydrouridine and anticodon loops (m2-guanine methyltransferase II) has a Ki of 0.3 muM, while m1-adenine methyltransferase shows intermediate sensitivity to SAH (Ki = 2.4 muM). All three methyltransferases have similar Km's for the S-adenosylmethionine substrate (1.5-2.0 muM). These results are consistent with the hypothesis that activity of individual tRNA methyltransferases may be controlled by enzyme systems which alter cellular SAH levels.
已从大鼠肝脏中分离并纯化出三种tRNA甲基转移酶，纯化倍数超过100倍。已检测这些酶对S-腺苷同型半胱氨酸（SAH）抑制作用的敏感性。在tRNA的二氢尿嘧啶环和受体茎之间区域形成m2-鸟嘌呤的甲基转移酶（m2-鸟嘌呤甲基转移酶I）对SAH抑制最不敏感，其Ki为8μM。负责在二氢尿嘧啶环和反密码子环之间形成m2-鸟嘌呤的酶（m2-鸟嘌呤甲基转移酶II）的Ki为0.3μM，而m1-腺嘌呤甲基转移酶对SAH表现出中等敏感性（Ki = 2.4μM）。所有三种甲基转移酶对S-腺苷甲硫氨酸底物的Km值相似（1.5 - 2.0μM）。这些结果与以下假设一致，即单个tRNA甲基转移酶的活性可能受改变细胞SAH水平的酶系统控制。
