title: Some kinetic properties of the tryptophan-sensitive 3-deoxy-D-arabino-heptulosonate 7-phosphate synthase from Neurospora crassa.
abstract: The steady-state kinetic properties of purified tryptophan-sensitive 3-deoxy-D-arabino-heptulosonate 7-phosphate synthase from Neurospora crassa were examined. The results suggest that the enzyme obeys a Rapid-Equilibrium Ordered mechanism, in which phosphoenolpyruvate is the first substrate to bind and 3-deoxy-D-arabino-heptulosonate 7-phosphate is the second product to be released, rather than a Ping Pong mechanism as has been reported previously. The inhibition by tryptophan was found to be parabolic competitive with respect to D-erythrose 4-phosphate and parabolic non-competitive with respect to phosphoenolpyruvate. The enzyme was inactivated by EDTA, and could be protected against this inactivation by phosphoenolpyruvate or 3-deoxy-D-arabino-heptulosonate 7-phosphate but not by D-erythrose 4-phosphate, tryptophan or Pi. This suggests that the enzyme may be a metalloenzyme.
mesh_terms: D010723:3-Deoxy-7-Phosphoheptulonate Synthase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D000446:Aldehyde-Lyases / Q000378:metabolism*; D004492:Edetic Acid / Q000494:pharmacology; D007700:Kinetics; D009491:Neurospora / Q000201:enzymology*; D009492:Neurospora crassa / Q000201:enzymology*; D010728:Phosphoenolpyruvate / Q000378:metabolism; D013403:Sugar Phosphates / Q000378:metabolism; D014364:Tryptophan / Q000494:pharmacology
chemical_list: D013403:Sugar Phosphates; C013469:3-deoxy-D-arabino-heptulosonate-7-phosphate; C026959:erythrose 4-phosphate; D010728:Phosphoenolpyruvate; D014364:Tryptophan; D004492:Edetic Acid; D010723:3-Deoxy-7-Phosphoheptulonate Synthase; D000446:Aldehyde-Lyases