Question

Briefly explain how Mg2+-dependent enzymes catalyse reactions of organophosphates such as adenosine triphosphate (ATP) with water and other nucleophiles.

Answer 1

• As ATP has a higher affinity for Mg2+ than ADP, the cytosolic magnesium concentration rises upon ATP hydrolysis.
• A large part of the intracellular pool of Mg2+ is present as MgATP. As the affinity of ATP for Mg2+ is about tenfold greater than that of ADP, ATP hydrolysis leads to a rise in [Mg2+]. The intracellular Mg2+ concentration typically more than doubles from its basal level.
• ATP-driven biomolecular motors utilize the chemical energy obtained from the ATP hydrolysis to perform vital tasks in living cells.
• ATP hydrolysis has high activation energy because it involves the breaking of two strong bonds, namely the Pγ–Oβγ bond of ATP and the H–O bond of lytic water.
• The magnesium ion neutralizes some of the negative charges present on the polyphosphate chain, reducing nonspecific ionic interactions between the enzyme and the polyphosphate group of the nucleotide.
• The interactions between the magnesium ion and the oxygen atoms in the phosphoryl group hold the nucleotide in well-defined conformations that can be specifically bound by the enzyme…
• The magnesium ion provides additional points of interaction between the ATP-Mg2+ complex and the enzyme, thus increasing the binding energy.

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