Purple acid phosphatases nucleophilic role

There are three mechanistic possibilities for catalysis by two-metal ion sites (Fig. 10). The first of these is the classic two-metal ion catalysis in which one metal plays the dominant role in activating the substrate toward nucleophilic attack, while the other metal ion furnishes the bound hydroxide as the nucleophile (Fig. 10 a). Upon substrate binding, the previously bridged hydroxide shifts to coordinate predominately with one metal ion. Enzymes believed to function through such a mechanism include a purple acid phosphatase [79], DNA polymerase I [80], inositol monophosphatase [81],fructose-1,6-bisphosphatase [82], Bam HI [83], and ribozymes [63]. 

Another phosphomonoesterase family, the purple acid phosphatases, have been attracting interest, since they contain a mixed-valence binu-clear iron(II/III) center (26). Although the exact roles of iron(II) and iron(III) have not been clarified yet, it has recently been reported that the direct nucleophilic attack of Fe111—OH- at the phosphate P atom is the most likely mechanism (27). 

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