Katoh H, Yoshinaga M, Yanagita T, Ohgi K, Irie M, Beintema J J, Meinsma D
Biochim Biophys Acta. 1986 Oct 17;873(3):367-71. doi: 10.1016/0167-4838(86)90085-3.
Kinetic constants for the transesterification of eight dinucleoside phosphates CpX and UpX by bovine and turtle pancreatic ribonuclease were determined. Both ribonucleases have a preference for purine nucleotides at the position X. However, bovine ribonuclease, like other mammalian ribonucleases, prefers 6-amino bases at this site, while turtle ribonuclease prefers 6-keto bases. This difference in specificity at the B2 site may be explained by the substitution of glutamic acid at position 111 by valine in turtle ribonuclease. These results have been confirmed by inhibition studies with the four nucleoside triphosphates. Inhibition studies with pT and pTp showed that a cationic binding group (P0) for the 5'-phosphate of the pyrimidine nucleotides bound at the primary B1 site is present in turtle ribonuclease, although lysine at position 66 in bovine ribonuclease is absent in turtle ribonuclease. However, the side chain of lysine 122 in turtle ribonuclease is probably located in the correct position to take over the role as cationic P0 site.
测定了牛和龟胰腺核糖核酸酶对8种二核苷磷酸CpX和UpX进行酯交换反应的动力学常数。两种核糖核酸酶对X位置的嘌呤核苷酸都有偏好。然而，牛核糖核酸酶与其他哺乳动物核糖核酸酶一样，在该位点更喜欢6-氨基碱基，而龟核糖核酸酶更喜欢6-酮基碱基。B2位点特异性的这种差异可能是由于龟核糖核酸酶中第111位的谷氨酸被缬氨酸取代所致。用四种核苷三磷酸进行的抑制研究证实了这些结果。用pT和pTp进行的抑制研究表明，龟核糖核酸酶中存在一个结合在主要B1位点的嘧啶核苷酸5'-磷酸的阳离子结合基团（P0），尽管龟核糖核酸酶中不存在牛核糖核酸酶第66位的赖氨酸。然而，龟核糖核酸酶中赖氨酸122的侧链可能位于正确位置，以承担阳离子P0位点的作用。
