Transfer of Energy Stored in Nucleotides

Nucleoside triphosphate-utilizing reactions may be classified in the following groups depending on the site of cleavage of the nucleoside triphosphate molecule and on the nature of the group transferred. In both biological and chemical systems, the a and y-phosphorus atoms are more susceptible to nucleophilic attack than is the /3-phosphorus. 

Phosphoryl group transfer is catalyzed by kinases (ATP-requiring phosphotransferases), of which a large number are known. The reaction involves nucleophilic attack by the acceptor on the y-phosphorus of ATP, with consequent cleavage between this phosphorus and the bridge oxygen atom. A divalent cation such as Mg + is required, and the dominant species present are MgATP (substrate) and ADP plus acceptor-POa (products). A number of such reactions require or are activated by K+. 

This group of enzyme reactions may be subdivided according to the nature of the acceptor molecule, as shown in Table 3-II. 

The transfer of the terminal pyrophosphoryl moiety of ATP is known to occur in only two cases. In both reactions is required to form MgATP, and phosphate is required as an activator its precise role is not yet known. 

Phosphoryl Group Transfer Reactions (Classified According TO Types of Acceptor Molecules) 

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