Pyrophospho group

The first step in coupling ATP cleavage to any process is transfer of part of the ATP molecule to a nucleophile Y, usually by displacement on one of the three phosphorus atoms. The nucleophilic attack may be (a) on the terminal phosphorus (Py) with displacement of ADP or (b) on the internal phosphorus (Pa) with displacement of inorganic pyrophosphate. In the first case, Y-P03H is formed in the latter, Y-adenylyl (sometimes shortened to Y-adenyl) is formed. More rarely, displacement occurs (c) on the central phosphorus (Pp) with transfer of a pyrophospho group to the... 

Ligases catalyze the joining together of two molecules, coupled to the hydrolysis of a pyrophospho-ryl group in ATP or a similar nucleoside triphosphate. 

Transfer of Phospho, Pyrophospho, and Adenylyl Groups from ATP... 

Isoprenyl pyrophosphates are synthesized by successive phosphorylation of mevalonate with ATP to yield the 5-monophosphate, 5-pyrophosphate, and 5-pyrophospho-3-monophospho derivatives. This last compound is very unstable and loses the 3-phosphate and the carboxyl group to yield isopentenyl pyrophosphate (IPPP), which is iso-merized to 3,3-dimethylallyl pyrophosphate (DMAPP). These reactions, catalyzed by cytosolic enzymes, are shown in Figure 19-13. 

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