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. 2016 Mar 8;291(17):8877–8884. doi: 10.1074/jbc.C115.699918

FIGURE 5.

FIGURE 5.

Scheme for the formation of PQQ from glutamate and tyrosine of PqqA. PqqA's conserved glutamate undergoes a hydrogen abstraction on the γ-carbon, forming a carbon radical that reacts with the 3-position of tyrosine to form a carbon-carbon bond. At this point, re-aromatization is favored, and the modified tyrosine loses a proton and electron, potentially to either the radical SAM cluster or an auxiliary cluster.