 These conformations are thought to be successive stages of a reaction pathway that requires subunit closure to bring the 2 molecules sufficiently close to react.PFK belongs to the phosphofructokinase B (PfkB) family of sugar kinases.Other members of this family (also known as the Ribokinase family) include ribokinase (RK) adenosine kinase (AK), inosine kinase, and 1-phosphofructokinase.