Sandbox Reserved 702: Difference between revisions

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The adenylyl cyclase reaction takes place in several steps: binding of ATP to the edema factor, enabling the deprotonation of 3'OH, stabilization of the penta-coordinated phosphorus intermediate and finally the release of cAMP and pyrophosphate. The enzyme binds its substrate, ATP and asparagine 583 interactss with it to restrict the rotation of the ribose. 3'OH is so hold in place for its nucleophilic attack durung the catalysis. Moreover, theprotonated histidine 351 stabilizes the HO- ion near the 3'OH group. Another model is that a neutral histidine deprotonates a water molecule and that the resulting HO- ion facilitates the deprotonation of 3'OH of ATP.

The magnesium ion that is coordinated by apsartates 491 and 493 and histidine 577 is localized near the 3'OH of ATP. Since it is positively charged, it stabilizes the negative charge of the 3'-oxyanion and thus facilitates the deprotonation of 3'OH. The action of this ion and of histidine 351 can be additive. To summarise, histidine 351 increases the local pH by attracting HO-, and the metal ion decreases the pKa of the 3'OH group. Maybe the magnesium ion also stabilizes the reaction intermediate by moving towards the non-bridging oxygen of α-phosphate durung the nucleophilic attack.

The second magnesium ion, that is coordinated with the oxygens of the phosphates of ATP, facilitates the bond breakage between α and β-phosphates. Indeed, it stabilizes the resulting negative charges. The stabilisation of the negative charged intermediate is also performed by different positive charged residues: arginine 329, lysine 353, lysine 372 and lysine 346.

Sandbox Reserved 702: Difference between revisions

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 The adenylyl cyclase reaction takes place in several steps: binding of ATP to the edema factor, enabling the deprotonation of 3'OH, stabilization of the penta-coordinated phosphorus intermediate and finally the release of cAMP and pyrophosphate. The enzyme binds its substrate, ATP and asparagine 583 interactss with it to restrict the rotation of the ribose. 3'OH is so hold in place for its nucleophilic attack durung the catalysis. Moreover, theprotonated histidine 351 stabilizes the HO- ion near the 3'OH group. Another model is that a neutral histidine deprotonates a water molecule and that the resulting HO- ion facilitates the deprotonation of 3'OH of ATP.
+The magnesium ion that is coordinated by apsartates 491 and 493 and histidine 577 is localized near the 3'OH of ATP. Since it is positively charged, it stabilizes the negative charge of the 3'-oxyanion and thus facilitates the deprotonation of 3'OH. The action of this ion and of histidine 351 can be additive. To summarise, histidine 351 increases the local pH by attracting HO-, and the metal ion decreases the pKa of the 3'OH group. Maybe the magnesium ion also stabilizes the reaction intermediate by moving towards the non-bridging oxygen of α-phosphate durung the nucleophilic attack.
+The second magnesium ion, that is coordinated with the oxygens of the phosphates of ATP, facilitates the bond breakage between α and β-phosphates. Indeed, it stabilizes the resulting negative charges. The stabilisation of the negative charged intermediate is also performed by different positive charged residues: arginine 329, lysine 353, lysine 372 and lysine 346.