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. Author manuscript; available in PMC: 2017 Jan 19.
Published in final edited form as: J Am Chem Soc. 2016 Nov 4;138(45):15004–15010. doi: 10.1021/jacs.6b09049

Figure 4.

Figure 4

Triple isotope effects measured on the STO rates of human heart LDH at 25 °C, pH/pD 4.3. The heavy enzyme, cofactor (NADD), and solvent (D2O) KIEs are synergistic with each other, suggesting that promoting vibrations, hydride transfer, and proton transfer occur in the same step. The protein mass-modulated promoting vibrations affect the barrier crossing probability but not the concerted mechanism of hydride–proton transfer in human heart LDH.