ON THE MECHANISM OF CATALYSIS BY RIBONUCLEASE - CLEAVAGE AND ISOMERIZATION OF THE DINUCLEOTIDE UPU CATALYZED BY IMIDAZOLE BUFFERS
ON THE MECHANISM OF CATALYSIS BY RIBONUCLEASE - CLEAVAGE AND ISOMERIZATION OF THE DINUCLEOTIDE UPU CATALYZED BY IMIDAZOLE BUFFERS
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DOI：
10.1021/ja00194a050
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发表时间：
1989-06-07
影响因子：
15
通讯作者：
BRESLOW, R
中科院分区：
文献类型：
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作者：
ANSLYN, E;BRESLOW, R
尿苷基(3'',5'')尿苷[(3'',5'')-UpU]在咪唑缓冲液的催化下裂解为尿苷2'',3''-环状磷酸和尿苷。动力学研究表明了连续的双功能机制，其中一种缓冲组分催化正膦单阴离子中间体的形成，另一种催化其向前分解成产物。通过对缓冲液催化的 (3'',5'')-UpU 异构化为 (2'',5'')-UpU 的研究，确定第一个催化剂为咪唑鎓离子，第二个催化剂为咪唑。由此产生的详细机制在化学上是合理的。它也与已知的牛胰腺核糖核酸酶一致。因此，也为酶促反应提出了相关的多步骤机制。
Uridylyl(3'',5'')uridine [(3'',5'')-UpU] undergoes cleavage to uridine 2'',3''-cyclic phosphate and uridine, catalyzed by imidazole buffers. Kinetic studies indicate a sequential bifunctional mechanisms, with one buffer component catalyzing the formation of a phosphorane monoanion intermediate and the other catalyzing its forward decomposition to products. From a study of the buffer-catalyzed isomerization of (3'',5'')-UpU to (2'',5'')-UpU, the first catalyst is identified as imidazolium ion and the second as imidazole. The resulting detailed mechanism is chemically reasonable. It is also consistent with what is known about bovine pancreatic ribonuclease. Thus, a related multistep mechanism is suggested for the enzymatic reactions as well.