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. Author manuscript; available in PMC: 2018 Apr 11.
Published in final edited form as: Biochemistry. 2017 Mar 31;56(14):2010–2023. doi: 10.1021/acs.biochem.7b00137

Figure 4. Substrate competition between PaFS and TbTS.

Figure 4

Relative product percentages for the generation of fusicoccadiene and taxadiene in reaction mixtures containing equimolar PaFS and TbTS. When the enzyme mixture is incubated with exogenous GGPP, the fusicoccadiene:taxadiene product ratio is 4.3:1. When the enzyme mixture is incubated with DMAPP and IPP, the only source of cyclization substrate GGPP is that generated by the C-terminal α domain of PaFS and the resulting fusicoccadiene:taxadiene product ratio increases to 46:1. That very little taxadiene is generated in this experiment strongly suggests a cluster channeling model for bifunctional catalysis, in which most of the GGPP generated remains bound in the PaFS hexamer to be utilized for cyclization to fusicoccadiene.