The final enzyme under consideration is pyrophosphatase. Inorganic phosphatase hydrolyzes inorganic pyrophosphate (PP_i) to two orthophosphates (P_i). This removes the inorganic pyrophosphates from biosynthetic reactions, which controls the level of (PP_i). This enzyme is dependent on metal cations such as Mg, Zn, Co, Mn, and Cd. Pyrophosphatase has up to four metal ions in its active site. They are bonded to the enzyme as metal activators while the others are liganded to the enzyme/substrate bonded product. These metal ions play a large role in the catalytic reaction, substrate activation, the acceptance of leaving groups, and the activation of water in the hydrolysis of the ether bond in the inorganic pyrophosphate. In the case of the pyrophosphatase from E. coli, the active site contained three Ca 2+ ions surrounded by the following residues: Glu31, Asp42, and Asp67. Overall, the hydrogen-bonding network found in the active site is formed by water with aspartates, glutamates, lysines, and tyrosines which participate in the binding of the substrate to the metal ions.

This enzyme has an alpha/beta which forms what appears to be a portion of a .

The active site consists of:

-four metal ions.

-the enzyme/substrate bonded product surrounded by residues , , and .

Hydrogen bonding then occurs between these residues and surrounding (all water molecules are within 3.0 angstroms) which leads to the binding of the substrate to the metal ions.

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