Sandbox Reserved 342: Difference between revisions
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=Introduction= | =Introduction= | ||
Xanthine-guanine Phosphoribosyltansferase (XGPRT) is one of three purine phosphoribosyltransferases (PRTases) that are part of the purine salvage pathway in ''Escherichia coli''<ref name="Vos"> PMID:9743633 </ref>; the other two PRTases in the pathway are HPRT and APRT<ref name="Vos"/> | Xanthine-guanine Phosphoribosyltansferase (XGPRT) is one of three purine phosphoribosyltransferases (PRTases) that are part of the purine salvage pathway in ''Escherichia coli''<ref name="Vos"> PMID:9743633 </ref>; the other two PRTases in the pathway are HPRT and APRT<ref name="Vos"/>. | ||
=Function= | =Function= | ||
XGPRT is an enzyme that catalyzes the conversion of guanine, xanthine, and sometimes hypoxanthine, to GMP, XMP, and IMP <ref name="Vos"/>. This enzyme is part of the purine salvage pathway, which converts exogenous purines (bases or nucleosides) to nucleotides in ''Escherichia coli''<ref name="Vos"/>. | XGPRT is an enzyme that catalyzes the conversion of guanine, xanthine, and sometimes hypoxanthine, to GMP, XMP, and IMP <ref name="Vos"/>. This enzyme is part of the purine salvage pathway, which converts exogenous purines (bases or nucleosides) to nucleotides in ''Escherichia coli''<ref name="Vos"/>. | ||
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=Mechanism and Catalysis= | =Mechanism and Catalysis= | ||
<Structure load='1a96' size='300' frame='true' align='right' caption='Xanthine-guanine Phosphoribosyltransferase' scene='Insert optional scene name here' /> | <Structure load='1a96' size='300' frame='true' align='right' caption='Xanthine-guanine Phosphoribosyltransferase' scene='Insert optional scene name here' /> | ||
The reaction catalyzed by XGPRT uses PRib-PP and a nitrogenous base to liberate a pyrophosphate and form a nucleoside monophosphate <ref name="Vos"/>. Magnesium and other divalent cations are necessary for catalysis because magnesium and PRib-PP binding play a critical role for the PRTase reaction<ref name="Vos"/>. The Mg:PRib-PP complex binds to the active site of PRTases<ref name="Vos"/>. XGPRT catalysis proceeds via SN1 mechanism and it forms a oxocarbonium ion in the transition state<ref name="Vos"/>. It has been suggested, that the magnesium ion departs with the displaced pyrophosphate because there is no magnesium ion at the active site, this has been determined by looking at crystal structures<ref name="Vos"/>. | |||
In the <scene name='Sandbox_Reserved_342/Mobile_loop/1'>mobile loop</scene> the XGPRT, there are several residues that are critical for substrate and catalysis<ref name="Vos"/>. The loop required for binding and catalysis is flexible, when XGPRT does not have products or substrates bound to it<ref name="Vos"/>. The flexibility of the residues in this loop assists movement of the loop towards the active site<ref name="Vos"/>. | In the <scene name='Sandbox_Reserved_342/Mobile_loop/1'>mobile loop</scene> the XGPRT, there are several residues that are critical for substrate and catalysis<ref name="Vos"/>. The loop required for binding and catalysis is flexible, when XGPRT does not have products or substrates bound to it<ref name="Vos"/>. The flexibility of the residues in this loop assists movement of the loop towards the active site<ref name="Vos"/>. | ||
=Additional Resources= | =Additional Resources= | ||