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. Author manuscript; available in PMC: 2018 Jul 19.
Published in final edited form as: Nat Prod Rep. 2018 Jul 18;35(7):660–694. doi: 10.1039/c8np00006a

Fig. 7.

Fig. 7

Moco biosynthesis and the mechanism of pyranopterin ring formation. (a) Overview of the Moco biosynthetic pathway. The symbols on GTP and cPMP indicate the source of the carbon and nitrogen atoms in cPMP as determined by isotope labeling studies.41,42 (b) Previously proposed functions for MoaA and MoaC, with MoaA catalyzing all the complex transformations required for the formation of the pyranopterin backbone structure of cPMP. (c) Revised functions for MoaA and MoaC, with MoaC catalyzing the complex rearrangement reactions to construct the pyranopterin structure, and MoaA catalyzing C3′-C8 bond formation.43 (d) The fate of C-8 in the biosynthesis of the other pterin containing molecules biopterin, folate and the flavins. In all these cases, the guanine C-8 is lost as formic acid.