Phosphoryl transfer reactions activated phosphates

Magnesium has its role intimately intertwined with phosphate in many phosphoryl transfer reactions, as Mg-ATP in muscle contraction, in the stabilization of nucleic acid structures as well as in the catalytic activity of ribozymes (catalytic RNA molecules). It also serves as a structural component of enzymes, and is found as the metal centre in chlorophylls, which absorbs light energy in photosynthesis. 

Further demonstrations of the effectiveness of particular cations in phosphoryl transfer reactions include the reduced activity of LiF, in contrast to other fluorides, in nucleophilic catalysis and the requirement for two Mg " ions in the enzymic hydrolysis of phosphate monoesters by inositol monophosphatase. ... 

Studies of hypervalent phosphorus compounds in biological phosphoryl transfer reactions include the preparation of novel anti-apicophilic penta-coordinated phosphoranes with frozen stereomutation using bulky biden-tate ligands. Kinetic studies have enabled the activation enthalpy of the stereomutation of an 0-equatorial phosphorane to its O-apical stereoisomer to be calculated. The involvement of hexacoordinated phosphoranes in phosphate transfer reactions has been clarified by theoretical calculations as well as in vitro studies. Applications of hexacoordinated compounds as catalysts have also been described. 

Since aspartyl phosphates have higher phosphorylating potentials than histidine phosphates, it was postulated that the [32P]polyP-phosphorylated Ca2+-ATPase could transfer the phosphate to a polyP chain as well as back to ADP. The capacity of the [32P]polyP phosphorylated Ca2+-ATPase to carry out these reactions was confirmed (Figure 22A,B), thus demonstrating that the CaATPase has all the enzymatic activities associated with polyphosphate kinases.129... 

Figure 1 Chemical mechanism of DNA polymerase and 3 -5 exonuclease, (a) DNA polymerase reaction. The enzyme chelates two metal Ions using three aspartic acid residues (only two are shown). Metal ion A abstracts the 3 hydroxyl proton of the primer terminus to generate a nucleophile that attacks the a-phosphate of an incoming dNTP substrate. The phosphoryl transfer results In production of a pyrophosphate leaving group, which is stabilized by metal Ion B. (b) The 3 -5 exonuclease proofreading activity is located in a site that is distinct from the polymerase site yet it uses two-metal-ion chemistry similar to DNA synthesis. The reaction type is hydrolysis in which metal ion A activates water to form the hydroxy anion nucleophile. Nucleophile attack on the phosphate of the mismatched nucleotide releases it as dNMP (dGMP in the case shown).

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