The 3-dehydroquinate synthase activity of the pentafunctional arom enzyme complex of Neurospora crassa is Zn2+-dependent.
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.
Lambert
J M
JM
Boocock
M R
MR
Coggins
J R
JR
D000429:Alcohol Oxidoreductases; D002614:Chelating Agents / Q000494:pharmacology; D004492:Edetic Acid / Q000494:pharmacology; D006836:Hydro-Lyases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D007700:Kinetics; D008190:Lyases; D009097:Multienzyme Complexes / Q000037:antagonists & inhibitors / Q000302:isolation & purification / Q000378:metabolism*; D009491:Neurospora / Q000201:enzymology*; D009492:Neurospora crassa / Q000201:enzymology*; D017853:Phosphotransferases (Alcohol Group Acceptor); D013403:Sugar Phosphates / Q000302:isolation & purification / Q000494:pharmacology; D014166:Transferases; D015032:Zinc / Q000494:pharmacology*
D002614:Chelating Agents; D009097:Multienzyme Complexes; D013403:Sugar Phosphates; C019728:arom enzyme; C013469:3-deoxy-D-arabino-heptulosonate-7-phosphate; D004492:Edetic Acid; D000429:Alcohol Oxidoreductases; D014166:Transferases; D017853:Phosphotransferases (Alcohol Group Acceptor); D008190:Lyases; D006836:Hydro-Lyases; C020000:3-dehydroquinate dehydratase; D015032:Zinc