کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
1316172 | 976431 | 2010 | 4 صفحه PDF | دانلود رایگان |
![عکس صفحه اول مقاله: Mononuclear and dinuclear mechanisms for catalysis of phosphodiester cleavage by alkaline earth metal ions in aqueous solution Mononuclear and dinuclear mechanisms for catalysis of phosphodiester cleavage by alkaline earth metal ions in aqueous solution](/preview/png/1316172.png)
In biological systems, enzymes often use metal ions, especially Mg2+, to catalyze phosphodiesterolysis, and model aqueous studies represent an important avenue of examining the contributions of these ions to catalysis. We have examined Mg2+ and Ca2+ catalyzed hydrolysis of the model phosphodiester thymidine-5′-p-nitrophenyl phosphate (T5PNP). At 25 °C, we find that, despite their different Lewis acidities, these ions have similar catalytic ability with second-order rate constants for attack of T5PNP by hydroxide (kOH) of 4.1 × 10−4 M−1s−1 and 3.7 × 10−4 M−1s−1 in the presence of 0.30 M Mg2+ and Ca2+, respectively, compared to 8.3 × 10−7 M−1s−1 in the absence of divalent metal ion. Examining the dependence of kOH on [M2+] at 50 °C indicates different kinetic mechanisms with Mg2+ utilizing a single ion mechanism and Ca2+ operating by parallel single and double ion mechanisms. Association of the metal ion(s) occurs prior to nucleophilic attack by hydroxide. Comparing the kOH values reveals a single Mg2+ catalyzes the reaction by 1800-fold whereas a single Ca2+ ion catalyzes the reaction by only 90-fold. The second Ca2+ provides an additional 10-fold catalysis, significantly reducing the catalytic disparity between Mg2+ and Ca2+.
Journal: Journal of Inorganic Biochemistry - Volume 104, Issue 2, February 2010, Pages 207–210