Pyrophosphate linkages

FIGURE 3.9 The triphosphate chain of ATP contains two pyrophosphate linkages, both of which release large amounts of energy upon hydrolysis. 

Additional steps occur in the case of eubacteria, namely syntheses of various dinucleotide forms of the cofactor, in which the pyranopterin is linked to a second nucleotide via a pyrophosphate linkage [34]. 

Several enzymic reactions that result in splitting of the pyrophosphate linkage and nucleophilic substitution at the phosphorus atom... 

Unlike the examples previously discussed, this interaction leads to splitting of the pyrophosphate linkage in the sugar nucleotide, with the liberation of nucleoside 5 -phosphate. Such reactions have been demonstrated for a-D-galactopyranosyl,468-488 2-acetamido-2-deoxy-a-D-glucopyranosyl,335,470 and pentapeptidyl-muramyl471,472 esters of uridine 5 -pyrophosphate. 

The characteristic high group transfer potential of a phospho group in pyrophosphate linkage, which makes ATP so useful in cells, also permits tetraethyl pyrophosphate to phosphorylate active sites of acetylcholinesterases. While TEPP is very toxic, it is rapidly hydrolyzed all harmful residues are gone within a few hours after use. 

The ATP molecule contains pyrophosphate linkages (bonds formed when two phosphate units are combined together) that release energy when needed. ATP can be hydrolyzed in two ways the removal of terminal phosphate to form adenosine diphosphate (ADP) and inorganic phosphate, or the removal of a terminal diphosphate to yield adenosine monophosphate (AMP) and pyrophosphate. The latter is usually cleaved further to yield two phosphates. This results in biosynthesis reactions, which do not occur alone, that can be driven in the direction of synthesis when the phosphate bonds are hydrolyzed. 

The difficulties encountered in the untemplated synthesis of natural nucleic acids is one factor that has prompted many researchers to propose alternatives to RNA as the initial genetic material. For example, a derivative of 3 -aminoguanosine can form untemplated chains of up to 20 bases in length.25 In addition, both cyclic and acyclic nucleotide bisphosphate derivatives polymerize without the aid of a template to form nucleic acids with pyrophosphate linkages between the monomers, rather than the more natural phosphodiester linkages.26-29... 

The rare earth complexes of octamethylpyrophosphoramide are the first examples of isolated complexes with rare earth ions coordinated to the pyrophosphate linkage. Experimental evidence supports the coordination of the phosphoryl oxygens to the metal ion with additional coordination positions occupied by water. 

Figure 26.1. Structure of CDP-Diacylglycerol. A key intermediate in the synthesis of phospholipids consists of phosphatidate and CMP joined by a pyrophosphate linkage. 

One suggested pathway cited in the above studies for the removal of pyrophosphate linkages from this oligomeric condensate was that ethylene oxide could react directly to insert itself into the pyrophosphate bond (17). This is illustrated in Eq. 2c of Fig. 

A DNA aptamer with iV-glycosylase activity has been isolated by in vitro selection." The catalytic rate enhancement is of the order of 10, and the aptamer catalyses the AT-glycosidic cleavage of a specific dG residue. It is dependent on divalent metal cations, and has optimal activity at pH 5. DNA aptamers that catalyse the capping of DNA with AMP to the 5 -end of the DNA, thus creating a 5, 5 -pyrophosphate linkage, have been evolved." The aptamers require Cu " and have a catalytic efficiency of 10 M min using either ATP or dATP. 

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