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.
Some kinetic properties of the tryptophan-sensitive 3-deoxy-d-arabino-heptulosonate 7-phosphate synthase from Neurospora crassa
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G A Nimmo, J R Coggins; Some kinetic properties of the tryptophan-sensitive 3-deoxy-d-arabino-heptulosonate 7-phosphate synthase from Neurospora crassa. Biochem J 1 December 1981; 199 (3): 657–665. doi: https://doi.org/10.1042/bj1990657
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