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. Author manuscript; available in PMC: 2009 Sep 23.
Published in final edited form as: Biochemistry. 2008 Aug 30;47(38):10111–10122. doi: 10.1021/bi8007164

Scheme 3.

Scheme 3

Proposed mechanism for stereospecific deprotonation of Cβ66 by general base catalysis involving Nη2 of Arg96. Carbanion formation is thought to trigger dehydration of the heterocycle, a process that may be facilitated by the Glu222 carboxylic acid as a proton donor.