We have demonstrated the co-purification in constant ratio of all five activities of the pentafunctional arom enzyme complex from Neurospora crassa. Progressive inactivation of the 3-dehydroquinate synthase component of the purified enzyme complex by chelating agents was blocked by the substrate, 3-deoxy-D-arabino-heptulosonate 7-phosphate, but not by the cofactor NAD+. Full activity was restored at Zn2+ concentrations as low as 0.05 nM. Atomic absorption data indicated that the intact enzyme complex contained 1 atom per subunit of tightly bound zinc. The arom 3-dehydroquinate synthase had a calculated turnover number of 19s-1, this being within the narrow range of values obtained for the other four activities of the intact multifunctional enzyme. The Km for 3-deoxy-D-arabino-heptulosonate 7-phosphate was 1.4 microM in a phosphate-free buffer; inorganic phosphate was a competitive inhibitor with respect to 3-deoxy-D-arabino-heptulosonate 7-phosphate.
The 3-dehydroquinate synthase activity of the pentafunctional arom enzyme complex of Neurospora crassa is Zn2+-dependent
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J M Lambert, M R Boocock, J R Coggins; The 3-dehydroquinate synthase activity of the pentafunctional arom enzyme complex of Neurospora crassa is Zn2+-dependent. Biochem J 15 March 1985; 226 (3): 817–829. doi: https://doi.org/10.1042/bj2260817
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