Nishio K, Kawakami M
Nucleic Acids Symp Ser. 1984(15):135-8.
Alanyl-tRNA synthetase of 115K dalton from Bombyx mori was cleaved into two fragments of 68K and 47K dalton with trypsin. The 47K fragment was active in aminoacylation of tRNA, whereas the 68K fragment inactive. The 47K and 68K fragments were located at the N- and C- terminal sides, respectively, in the intact enzyme. When the enzyme binds alanine specific tRNA, the tryptic digestion is inhibited. The Km value of the 47K fragment for tRNA was about 16-fold higher than that (1.4 microM) of the intact enzyme. The molecular activities of the 47K fragment and the intact enzyme were 2.2/sec and 16.8/sec, respectively. These results show that 1) Bombyx mori alanyl-tRNA synthetase functions in a monomeric state and 2) the C-terminal domain enhances affinity for tRNA and is responsible for full activity of aminoacylation.
家蚕115K道尔顿的丙氨酰 - tRNA合成酶被胰蛋白酶切割成68K和47K道尔顿的两个片段。47K片段在tRNA的氨酰化反应中具有活性，而68K片段无活性。在完整的酶中，47K和68K片段分别位于N端和C端。当该酶结合丙氨酸特异性tRNA时，胰蛋白酶消化受到抑制。47K片段对tRNA的Km值比完整酶的Km值（1.4 microM）高约16倍。47K片段和完整酶的分子活性分别为2.2/秒和16.8/秒。这些结果表明：1）家蚕丙氨酰 - tRNA合成酶以单体状态发挥作用；2）C端结构域增强了对tRNA的亲和力，并负责氨酰化的全部活性。
