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Figure 1.
Figure 1. The conversion of chorismate to salicylate and
pyruvate occurs in two steps, the conversion of chorismate to
isochorismate, catalyzed by ischorismate synthases, and the
conversion of isochorismate to salicylate and pyruvate,
catalyzed by isochorismate pyruvate lyases. Irp9 has been shown
to catalyze both reactions converting chorismate to salicylate
via isochorismate.10 Two alternative mechanisms for the pyruvate
lyase reactions are shown. In mechanism (a) the acidic (AH) and
basic (B) groups are proposed to be Tyr372 and His321,
respectively. Mechanism (b) is based on a recent proposal for
PchB, a pyruvate lyase.25^ and 26
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