Scheme 1.

Models for the kinetic mechanism of Escherichia coli asparagine synthetase B. (Top) Proposed kinetic mechanism based on product inhibition and isotope trapping experiments (model I) (Middle). Model I modified to include the leakage of ammonia from the intramolecular tunnel (model II). (Bottom) Modified proposal for the AS-B kinetic mechanism that assumes catalytic site coordination after βAspAMP formation and no leakage of ammonia from the intramolecular tunnel (model III). The models are reproduced from Tesson et al. (2003) with permission