Phosphate stabilization divalent metals

Fructose 1,6-diphosphatase hydrolyzes D-fructose 1,6-diphosphate to give D-fructose 6-phosphate and PO . It is a key enzyme in the gluconeo-genesis pathway. Two divalent metal ions (Mg2+, Mn2+, Zn2+, and Co2+) are involved in catalysis. In the enzyme isolated from pork kidney the metal-metal distance accounts to 3.7 A [12]. A reaction mechanism similar to that of protein phosphatase 1 was proposed, but leaving group stabilization by metal coordination of the ester oxygen atom appears to be absent (Figure 6) [12]. 

Polynucleotide polymerases, or nucleotidyl transferases, are enzymes that catalyze the template-instructed polymerization of deoxyribo- or ribonu-cleoside triphosphates into polymeric nucleic acid - DNA or RNA. Depending on their substrate specificity, polymerases are classed as RNA- or DNA-dependent polymerases which copy their templates into RNA or DNA (all combinations of substrates are possible). Polymerization, or nucleotidyl transfer, involves formation of a phosphodiester bond that results from nucleophilic attack of the 3 -OH of primer-template on the a-phosphate group of the incoming nucleoside triphosphate. Although substantial diversity of sequence and function is observed for natural polymerases, there is evidence that many employ the same mechanism for DNA or RNA synthesis. On the basis of the crystal structures of polymerase replication complexes, a two-metal-ion mechanism of nucleotide addition was proposed [1] during this two divalent metal ions stabilize the structure and charge of the expected pentacovalent transition state (Figure B.16.1). 

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