Landin R M, Rousseau N
Biochimie. 1976;58(11-12):1337-44. doi: 10.1016/s0300-9084(77)80017-5.
Foetal rat liver extracts were found to have higher tRNA methylene activities than corresponding extracts of adult liver. When the specific activities were expressed per mg of liver or per mg of protein, the foetal tRNA methylating enzymes were respectively 2.5 and 6 times higher than those of adult livers. The presence of an inhibitor in adult liver can be excluded, since the same recoveries of total tRNA methylase activity were obtained after partial purification of both adult and foetal liver extracts: yields were close to 100%. The apparent Km's for the substrates in the methylating reactions were the same when tRNA methylases from either adult or foetal liver were used: values were 0.2 muM for Escherichia coli tRNA and 2.1 muM for S-adenosyl-L-methionine. After T1-T2 ribonuclease digestion of an in vitro methylated tRNA, similar methyl nucleotide patterns were observed in foetal and adult enzymatic extracts. It is concluded that the same tRNA methylase pool is present in adult and foetal liver. In addition, it is hypothesized that the different reaction rates exhibited by these enzymes might be due to the tRNA functional requirements rather than to the presence of a tRNA methylase inhibitor.
已发现胎鼠肝脏提取物的tRNA亚甲基化活性高于相应的成年肝脏提取物。当以每毫克肝脏或每毫克蛋白质表示比活性时，胎儿tRNA甲基化酶分别比成年肝脏的高2.5倍和6倍。由于对成年和胎儿肝脏提取物进行部分纯化后获得的总tRNA甲基化酶活性回收率相同：产率接近100%，因此可以排除成年肝脏中存在抑制剂。当使用来自成年或胎儿肝脏的tRNA甲基化酶时，甲基化反应中底物的表观Km值相同：大肠杆菌tRNA的值为0.2μM，S-腺苷-L-甲硫氨酸的值为2.1μM。对体外甲基化的tRNA进行T1-T2核糖核酸酶消化后，在胎儿和成年酶提取物中观察到相似的甲基核苷酸模式。结论是成年和胎儿肝脏中存在相同的tRNA甲基化酶库。此外，据推测，这些酶表现出的不同反应速率可能是由于tRNA的功能需求，而不是由于存在tRNA甲基化酶抑制剂。
