Pyruvate/Phosphoenolpyruvate kinase <p>Pyruvate kinase controls the exit from the glysolysis pathway, catalysing the transfer of phosphate from phosphooenolpyruvate (PEP) to ADP. Mammalian pyruvate kinase is a homotetramer, where each polypeptide subunit consists of four domains: N-terminal, A domain, B domain and C-terminal. Activation of the enzyme is believed to occur via the clamping down of the B domain onto the A domain to dehydrate the active site cleft. The N- and C-terminal domains are situated at inter-subunit contact sites, and could be involved in assembly and communication within the complex. The N-terminal domain has a TIM beta/alpha-barrel structure. Homologous TIM-barrel domains are found in the following proteins:</p><ul><li>N-terminal of pyruvate kinase (<db_xref db="EC" dbkey="2.7.1.40"/>), which is interrupted by an all-beta domain [<cite idref="PUB00024777"/>].</li><li>C-terminal of pyruvate phosphate dikinase (<db_xref db="EC" dbkey="2.7.9.1"/>), which has a similar mode of substrate binding to pyruvate kinase [<cite idref="PUB00026675"/>].</li><li>Phosphoenolpyruvate carboxylase (<db_xref db="EC" dbkey=" 4.1.1.31"/>); this domain has additional helices [<cite idref="PUB00026498"/>].</li><li>Phosphenolpyruvate mutase(<db_xref db="EC" dbkey="5.4.2.9"/>)/Isocitrate lyase (<db_xref db="EC" dbkey=" 4.1.3.1"/>), where it forms a swapped dimer [<cite idref="PUB00028676"/>].</li><li>HpcH/HpaI aldolases, such as the beta subunit of citrate lyase, where it forms a swapped dimer, and contains a pyruvate kinase-type metal binding site [<cite idref="PUB00035541"/>].</li><li>Ketopantoate hydroxymethyltransferase PanB (<db_xref db="EC" dbkey=" 2.1.2.11"/>), where a C-terminal helix exchange is observed in some enzymes [<cite idref="PUB00022133"/>].</li></ul>