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Phosphofructokinase, a key regulatory enzyme in glycolysis, catalyzes the phosphorylation of fructose-6-phosphate to fructose-1,6-biphosphate. The members belong to PFK family that includes ATP- and pyrophosphate (PPi)- dependent phosphofructokinases. Some members evolved by gene duplication and thus have a large C-terminal/N-terminal extension comprising a second PFK domain. Generally, ATP-PFKs are allosteric homotetramers, and PPi-PFKs are dimeric and nonallosteric except for plant PPi-PFKs which are allosteric heterotetramers.