Machuga E, Klapper M H
J Biol Chem. 1975 Mar 25;250(6):2319-23.
Ntau-Carboxymethylhistidine-12 RNase is active with both RNA and uridine cyclic 2':3'-monophosphate as substrates. Experimental evidence is presented to show that the activity cannot be due to contaminating RNase A, or other RNase-type protein, to the presence of a mixed dimer between 12- and 119-substituted RNases, or to the presence of trace amounts of Ntau-carboxymethylhistidine-12 RNase. The carboxymethyl derivative has approximately 1 and 13 per cent the specific activity of native enzyme against cyclic 2',3'-UMP at pH 5.0 and 8.5, respectively.
Nτ-羧甲基组氨酸-12核糖核酸酶以RNA和尿苷环2':3'-单磷酸作为底物时均具有活性。实验证据表明，该活性并非源于污染的核糖核酸酶A或其他核糖核酸酶类型的蛋白质，也不是由于12位和119位取代的核糖核酸酶之间存在混合二聚体，或痕量Nτ-羧甲基组氨酸-12核糖核酸酶的存在。在pH 5.0和8.5条件下，羧甲基衍生物对环2',3'-UMP的比活性分别约为天然酶的1%和13%。
