The active site similiarities, including a water coordinated to two metal ions, suggest that the family II PPase mechanism is "analogous" (not "homologous") to that of family I PPases. This is a remarkable example of convergent evolution. The large change in C-terminal conformation suggests that domain closure might be the mechanism by which Sm-PPase achieves specificity for pyrophosphate over other polyphosphates.

Pyrophosphatase (PPase) from Bacillus subtilis has recently been found to be the first example of a family II soluble PPase with a unique requirement for Mn 2؉ . In the present work, we cloned and overexpressed in Escherichia coli putative genes for two more family II PPases (from Streptococcus mutans and Streptococcus gordonii), isolated the recombinant proteins, and showed them to be highly specific and active PPases (catalytic constants of 1700 -3300 s ؊1 at 25°C in comparison with 200 -400 s ؊1 for family I). All three family II PPases were found to be dimeric manganese metalloenzymes, dissociating into much less active monomers upon removal of Mn 2؉ . The dimers were found to have one high affinity manganese-specific site (K d of 0.2-3 nM for Mn 2؉ and 10 -80 M for Mg 2؉ ) and two or three moderate affinity sites (K d ϳ 1 mM for both cations) per subunit. Mn 2؉ binding to the high affinity site, which occurs with a half-time of less than 10 s at 1.5 mM Mn 2؉ , dramatically shifts the monomer 7 dimer equilibrium in the direction of the dimer, further activates the dimer, and allows substantial activity (60 -180 s ؊1 ) against calcium pyrophosphate, a potent inhibitor of family I PPases.

Endometrial or endometriotic tissue E2 concentrations are actively regulated by local estrogen metabolism in the tissue. Thus, the inhibition of local E2 synthesis is a valid, novel approach to reduce local E2-dependent growth of endometriotic tissue.

An open reading frame located in the COTF-TETB intergenic region of Bacillus subtilis was cloned and expressed in Escherichia coli and shown to encode inorganic pyrophosphatase (PPase). The isolated enzyme is Mn P+ -activated, like the authentic PPase isolated from B. subtilis. Although 13 functionally important active site residues are conserved in all 31 soluble PPase sequences so far identified, only two of them are conserved in B. subtilis PPase. This suggests that B. subtilis PPase represents a new family of soluble PPases (a Bs family), putative members of which were found in Archaeoglobus fulgidus, Methanococcus jannaschii, Streptococcus mutans and Streptococcus gordonii.z 1998 Federation of European Biochemical Societies.

Based on the primary structure, soluble inorganic pyrophosphatases can be divided into two families which exhibit no sequence similarity to each other. Family I, comprising most of the known pyrophosphatase sequences, can be further divided into prokaryotic, plant and animal/fungal pyrophosphatases. Interestingly, plant pyrophosphatases bear a closer similarity to prokaryotic than to animal/fungal pyrophosphatases. Only 17 residues are conserved in all 37 pyrophosphatases of family I and remarkably, 15 of these residues are located at the active site. Subunit interface residues are conserved in animal/fungal but not in prokaryotic pyrophosphatases.z 1999 Federation of European Biochemical Societies.