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. 2019 Jan 31;141(8):3320–3331. doi: 10.1021/jacs.8b10836

Figure 1.

Figure 1

Dianion-activated proton- and hydride-transfer reactions catalyzed by TIM (reactions on the left) and by GPDH (reactions on the right). TIM catalyzes isomerization of the whole substrate glyceraldehyde 3-phosphate (GAP) to form dihydroxyacetone phosphate (DHAP)62 and exchange between deuterium in D2O and the α-carbonyl hydrogen of the substrate piece glycolaldehyde (GA) that is activated by the second piece of phosphite dianion (HPi = HPO32–).54,63 GPDH catalyzes reduction of the whole substrate DHAP by NADH to form l-glycerol 3-phosphate (G3P) and reduction of GA by NADH to form ethylene glycol (EG) that is activated by HPi.55 In each case phosphite dianion binds weakly to free enzyme, while the transition state for the reactions of the whole substrate is stabilized by 11–12 kcal/mol by interactions with the substrate phosphodianion, and the transition state for reaction of the truncated substrate is stabilized by 6–8 kcal/mol by interactions with the phosphite dianion.51