 It was previously thought that the mechanism of action for adenylosuccinate lyase was a concerted catalysis where the hydrogen on the β-carbon (with respect to the leaving nitrogen) was abstracted by the catalytic base at the same time that the leaving nitrogen was protonated by the catalytic acid for E2 elimination.More recent data conflicts with this idea and has confirmed that the mechanism is not in fact concerted, but that the abstraction occurs first and there is an intermediate carbanion species which is resonance stabilized.For both ASL-catalyzed reactions deprotonation of the carbon β to the leaving nitrogen occurs first, then the formation and resonance stabilization of the carbanion occurs, and lastly the protonation of the leaving nitrogen which causes the C-N bond to break.