Dinuclear Zn<sup>2+</sup>complexes in the hydrolysis of the phosphodiester linkage in a diribonucleoside monophosphate diester
作者:Morio Yashiro、Hideki Kaneiwa、Kenichi Onaka、Makoto Komiyama
DOI:10.1039/b312301d
日期:——
Dizinc complexes that were formed from 2 ∶ 1 mixtures of Zn(NO3)2 and dinucleating ligands TPHP (1), TPmX (2) or TPpX (3) in aqueous solutions efficiently hydrolyzed diribonucleoside monophosphate diesters (NpN) under mild conditions. The dinucleating ligand affected the structure of the aquo-hydroxo-dizinc core, resulting in different characteristics in the catalytic activities towards NpN cleavage. The pH-rate profile of ApA cleavage in the presence of (Zn2+)2-1 was sigmoidal, whereas those of (Zn2+)2-2 and (Zn2+)2-3 were bell-shaped. The pH titration study indicated that (Zn2+)2-1 dissociates only one aquo proton (up to pH 12), whereas (Zn2+)2-2 dissociates three aquo protons (up to pH 10.7). The observed differences in the pH-rate profile are attributable to the various distributions of the monohydroxo-dizinc species, which are responsible for NpN cleavage. As compared to that using (Zn2+)2-1, the NpN cleavage using (Zn2+)2-2 showed a greater rate constant, with a higher product ratio of 3′-NMP/2′-NMP. The saturation behaviors of the rate, with regard to the concentration of NpN, were analyzed by Michaelis–Menten type kinetics. Although the binding of (Zn2+)2-2 to ApA was weaker than that of (Zn2+)2-1, (Zn2+)2-2 showed a greater kcat value than (Zn2+)2-1, resulting in higher ApA cleavage activity of the former.
由2:1的Zn(NO3)2与双配体TPHP(1)、TPmX(2)或TPpX(3)在水溶液中形成的二锌复合物在温和条件下有效水解二核苷酸单磷酸二酯(NpN)。双配体的结构影响了水合羟基二锌核心的构造,导致其催化NpN裂解的活性特征有所不同。在(Zn2+)2-1存在下,ApA裂解的pH-速率曲线呈S型,而(Zn2+)2-2和(Zn2+)2-3的曲线则呈钟形。pH滴定研究表明,(Zn2+)2-1仅在pH达到12时解离一个水合质子,而(Zn2+)2-2在pH达到10.7时则解离三个水合质子。观察到的pH-速率曲线差异可归因于单羟基二锌物种的不同分布,这些物种是NpN裂解的关键。与使用(Zn2+)2-1相比,使用(Zn2+)2-2时的NpN裂解表现出更大的速率常数,且3′-NMP/2′-NMP的产物比例更高。关于NpN浓度的速率饱和行为通过米氏动力学分析。尽管(Zn2+)2-2对ApA的结合强度弱于(Zn2+)2-1,但(Zn2+)2-2的kcat值高于(Zn2+)2-1,导致前者在ApA裂解中的活性更强。