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. Author manuscript; available in PMC: 2011 Apr 1.
Published in final edited form as: Bioorg Chem. 2009 Nov 29;38(2):62–73. doi: 10.1016/j.bioorg.2009.11.004

Fig. 2.

Fig. 2

Proposed catalytic mechanism: Cys324 is the active site nucleophile and His202 acts as a general acid, donating a proton to the departing amine, leading to the formation of an S-alkyl thiouronium intermediate. His 202 activates a water molecule for nucleophilic attack on the thiouronium intermediate. This leads to the formation of a second tetrahedral intermediate that collapses to eliminate the Cys thiolate and generate NCP.