Amino acid activation, inorganic pyrophosphatase

In 1998 the long-known Bacillus subtilis inorganic pyrophosphatase was characterized and found to have much greater activity than the above enzymes, to have a completely different amino acid sequence, not to be inhibited by F and to be activated by This form of... 

The splitting of inorganic pyrophosphafe (PPj) into two inorganic phosphate ions is catalyzed by pyrophosphatases (p. 636) that apparently occur universally. Their function appears to be simply to remove the product PPj from reactions that produce it, shifting the equilibrium toward formation of a desired compound. An example is the formation of aminoacyl-tRNA molecules needed for protein synthesis. As shown in Eq. 17-36, the process requires the use of two ATP molecules to activate one amino acid. While the "spending" of two ATPs for the addition of one monomer imif to a polymer does not appear necessary from a thermodynamic viewpoint, it is frequently observed, and there is no doubt that hydrolysis of PP ensures thaf the reaction will go virtually to completion. Transfer RNAs fend to become saturated with amino acids according to Eq. 17-36 even if the concentration of free amino acid in the cytoplasm is low. On the other hand, kinetic considerations may be involved. Perhaps the biosynthetic sequence would move too slowly if if were nof for the extra boost given by the removal of PPj. Part of the explanation for the complexity may depend on control mechanisms which are only incompletely understood. 

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