MG2-COLI INORGANIC PYROPHOSPHATASE( ACTIVATION OF ESCHERICHIA)

Further refinement of X-ray data on Escherichia coli inorganic pyropho sphatase [Oganessyan et al, (1994) FEES Lett, 348, 301-304] to 2.2 Ang strom reveals a system of noncovalent interactions involving Tyr(55) a nd Tyr(141) in the active site, The pK(a) for one of the eight Tyr res idues in wild-type pyrophosphatase is as low as 9.1 and further decrea ses to 8.1 upon Mg2+ binding, generating characteristic changes in the absorption spectrum, These effects are lost in a Y55F but not in a Y1 41F variant, It is suggested that the lower-affinity site for Mg2+ in the enzyme is formed by Tyr(55) and Asp(70), which are in close proxim ity in the ape-enzyme structure.