Which element is required by phosphofructokinase?

Phosphofructokinase (PFK) is --300 amino acids in length, and structural studies of the bacterial enzyme have shown it comprises two similar (alpha/beta) lobes: one involved in ATP binding and the other housing both the substrate-binding site and the allosteric site (a regulatory binding site distinct from the active site, but that affects enzyme activity). The identical tetramer subunits adopt 2 different conformations: in a 'closed' state, the bound magnesium ion bridges the phosphoryl groups of the enzyme products (ADP and fructose-1,6- bisphosphate); and in an 'open' state, the magnesium ion binds only the ADP, as the 2 products are now fuher apa