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. Author manuscript; available in PMC: 2016 Dec 8.
Published in final edited form as: Biochemistry. 2015 Nov 25;54(48):7110–7119. doi: 10.1021/acs.biochem.5b00958

Table 3.

pKa Values and pKa Isotope Effects of D40N-Cl-Y Variants

D40N D40N-Cl-Y57 D40N-Cl-Y32 D40N-Cl-Y16
pKa (H) 5.78 ± 0.11 5.15 ± 0.08 5.66 ± 0.08 4.86 ± 0.13
pKa (D) 6.65 ± 0.09 5.76 ± 0.07 6.53 ± 0.08 5.56 ± 0.04
pKa shift relative to D40Na – −0.65 (+1.22b) −0.10 −0.90
H–D pKa isotope effect (ΔpKa) 0.87 ± 0.14 0.61 ± 0.10 0.87 ± 0.11 0.70 ± 0.14
shift in H–D pKa isotope effect relative to D40Na – −0.26 ~0 −0.17
primary site of titration Y57 Cl-Y57 Y57 Y57
a

The pKa and isotope effect of D40N are used as the reference states for comparison.

b

The partial contribution to the pKa shift from the loss of proton delocalization (see the text).