over the active site, preventing the escape of reaction intermediates or undesirable side reactions. Binding of phosphate alone is not capable of causing a transition between the open and closed states. A third, "partially open" intermediate has also been reported upon binding of DXP alone. pdxJ assembles as an octamer under biological conditions. This octamer can be thought of as a tetramer of dimers, and it is likely that the dimer is the active unit of the protein. In each dimer, an arginine residue Arg20 forms part of the active site in the other monomer, where it helps bind both phosphate groups. Classification This enzyme belongs to the family of transferases, specifically those transferring nitrogenous groups transferring other nitrogenous groups. Nomenclature The systematic name of this enzyme class is 1-deoxy-D-xylulose-5-phosphate:3-amino-2-oxopropyl phosphate 3-amino-2-oxopropyltransferase (phosphate-hydrolysing; cyclizing). Other names in common use include pyridoxine 5-phosphate phospho lyase, PNP synthase, and PdxJ. Biological role This enzyme participates in vitamin B6 metabolism. pdxJ plays a role in the DXP-dependent pathway of pyridoxal phosphate. The DXP-dependent pathway is found predominantly in Gammaproteobacteria and some Alphaproteobacteria. Because of this distribution, pdxJ has been identified as a potential drug target for antibiotics. This identification seems to have validity, as other approaches have also identified pdxJ as a good target for drug development. However, there may be limits to this approach as pdxJ is not found in obligate parasites. pdxJ and more generally vitamin B6 metabolism in the microbiome have also been shown to alter the effects of certain compounds on animal hosts. References EC 2.6.99 Enzymes of unknown structure