Phosphofructokinase, conserved site The enzyme-catalysed transfer of a phosphoryl group from ATP is animportant reaction in a wide variety of biological processes [<cite idref="PUB00004002"/>]. Oneenzyme that utilises this reaction is phosphofructokinase (PFK), whichcatalyses the phosphorylation of fructose-6-phosphate to fructose-1,6-bisphosphate, a key regulatory step in the glycolytic pathway [<cite idref="PUB00014238"/>, <cite idref="PUB00000020"/>]. PFK exists as a homotetramer in bacteria and mammals (where each monomerpossesses 2 similar domains), and as an octomer in yeast (where there are4 alpha- (PFK1) and 4 beta-chains (PFK2), the latter, like the mammalianmonomers, possessing 2 similar domains [<cite idref="PUB00000020"/>]). <p>PFK is ~300 amino acids in length, and structural studies of thebacterial enzyme have shown it comprises two similar (alpha/beta) lobes: one involved inATP 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 enzymeactivity). The identical tetramer subunits adopt 2 different conformations: in a 'closed' state, the bound magnesium ionbridges 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[<cite idref="PUB00003237"/>], as the 2 products are now further apart. These conformations arethought to be successive stages of a reaction pathway that requires subunitclosure to bring the 2 molecules sufficiently close to react [<cite idref="PUB00003237"/>].</p><p>Deficiency in PFK leads to glycogenosis type VII (Tauri's disease), anautosomal recessive disorder characterised by severe nausea, vomiting,muscle cramps and myoglobinuria in response to bursts of intense orvigorous exercise [<cite idref="PUB00000020"/>]. Sufferers are usually able to lead a reasonablyordinary life by learning to adjust activity levels [<cite idref="PUB00000020"/>].</p><p>This entry represents a region located in the C terminus that contains three basic residues involved in fructose-6-phosphate binding.</p>