Quinolinic acid is an intermediate in the biosynthesis of nicotinamide-containing redox cofactors. The ultimate step in the formation of quinolinic acid in prokaryotes is the condensation of iminosuccinate and dihydroxyacetone phosphate, which is catalyzed by the product of the nadA gene in Escherichia coli. A combination of UV-vis, Mössbauer, and EPR spectroscopies, along with analytical methods for the determination of iron and sulfide, demonstrates for the first time that anaerobically purified quinolinate synthetase (NadA) from E. coli contains one [4Fe-4S] cluster per polypeptide. The protein is active, catalyzing the formation of quinolinic acid with a Vmax [ET]-1 of 0.01 s-1.
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