ABSTRACT
Phosphomonoesterases are enzymes which are responsible for the hydrolytic cleavage of single phosphate groups from a variety of substrates. They can be distinguished from other enzymes which act on phosphate groups, such as phosphodiesterases, pyrophosphatases and ATPases, in that one of the products of the reaction is always free inorganic phosphate and the other is a dephosphorylated organic molecule. Thermodynamically such reactions are effectively irreversible in biological systems and different enzymes, such as the various kinases, are responsible for the addition of phosphate groups to biomolecules. Phosphomonoesterases are commonly known as phosphatases. An example of a phosphomonoesterase is non-specific acid phosphatase (EC 3.1.3.2.) which can be assayed using the artificial substrate p-nitrophenyl phosphate:
p-nitrophenyl phosphate+H2O→p-nitrophenol+inorganic phosphate
The two main roles of phosphomonoesterases are either in removing the phosphate group from the substrate so that the product can then be used in other ways, for example as a biosynthetic precursor, or in providing a source of free phosphate itself. These roles can be broadly characterized as digestive and nutritive. However, other more specialized roles do exist, for example the regulatory effects exerted by specific phosphoprotein phosphatases.
