Hashimoto J, Takahashi K
J Biochem. 1977 Apr;81(4):1175-80. doi: 10.1093/oxfordjournals.jbchem.a131544.
In order to obtain information on the nature of the amino acid residues involved in the activity of ribonuclease U1 [EC 3.1.4.8], various chemical modifications of the enzyme were carried out. RNase U1 was inactivated by reaction with iodoacetate at pH 5.5 with concomitant incorporation of 1 carboxymethyl group per molecule of the enzyme. The residue specifically modified by iodoacetate was identified as one of the glutamic acid residues, as in the case of RNase T1. The enzyme was also inactivated extensively by reaction with iodoacetamide at pH 8.0 with the loss of about one residue each of histidine and lysine. When RNase U1 was treated with a large excess of phenylglyoxal, the enzymatic activity and binding ability toward 3'-GMP were lost, with simultaneous modification of about 1 residue of arginine. The reaction of citraconic anhydride with RNase U1 led to the loss of enzymatic activity and modification of about 1 residue of lysine. The inactivated enzyme, however, retained binding ability toward 3'-GMP. These results indicate that there are marked similarities in the active sites of RNases T1 and U1.
为了获取有关参与核糖核酸酶U1[EC 3.1.4.8]活性的氨基酸残基性质的信息，对该酶进行了各种化学修饰。核糖核酸酶U1在pH 5.5下与碘乙酸反应而失活，每分子酶同时掺入1个羧甲基。经碘乙酸特异性修饰的残基被鉴定为谷氨酸残基之一，如同核糖核酸酶T1的情况。该酶在pH 8.0下与碘乙酰胺反应也会大量失活，同时组氨酸和赖氨酸各损失约1个残基。当用大量过量的苯乙二醛处理核糖核酸酶U1时，其酶活性和对3'-GMP的结合能力丧失，同时约1个精氨酸残基被修饰。柠康酸酐与核糖核酸酶U1的反应导致酶活性丧失和约1个赖氨酸残基被修饰。然而，失活的酶仍保留对3'-GMP的结合能力。这些结果表明，核糖核酸酶T1和U1的活性位点存在明显相似性。
