Table 2.

Comparison of best-fit parameters with literature deuterium KIEs associated with NADPH dehydrogenases and transhydrogenases

		Best fit values†					Literature values
Enzyme	Pathway	Parameter‡	Ratio	$\alpha$	${\delta }^2$H,§ ‰	$ϵ$,¶ ‰	$ϵ$,∥‰	In vitro KIE	Ref.
G6PDH	PP and ED	${\mathrm{R}}_G$	7.05 $\times$ 10−5	—	$-547$	$-508$	$-663$	2.97	(45)
6PGDH	PP	${\mathrm{R}}_P$	1.08 $\times$ 10−4	—	$-305$	$-244$	$-379$	1.61	(46)
ICDH	TCA cycle	${\mathrm{R}}_I$	2.99 $\times$ 10−4	—	$+918$	+1,085	$\sim$0	$\sim$1	(26, 42, 47)
ME	Anaplerotic node	${\mathrm{R}}_M$	0.00	—	—	—	$-320$	1.47	(45)
PntAB	—	${\mathrm{R}}_U$	3.46 $\times$ 10−5	—	$-778$	$-758$	$-444$ to $-778$	1.8–4.5	(27)
unknown	—	${\mathrm{R}}_U^{*}$	0.00	—	—	—	—	—	—
UdhA	—	${\alpha }_O$	—	0.84	—	$-160$	—	—	—
sTH or other	—	${\alpha }_O^{*}$	—	0.57	—	$-434$	—	—	—

^†Best-fit parameters were derived by minimizing the rms difference between experimental data and predicted lipid ${\delta }^2$H values from Eqs. 1–3. Uncertainties associated with these values are discussed in SI Appendix, Fig. S4.

^‡$R_{\mathrm{U}}$ and ${\alpha }_{\mathrm{O}}$ account for the membrane-bound (PntAB) and soluble (UdhA) transhydrogenase from E. coli, respectively. ${\alpha }_{\mathrm{O}}^{*}$ account for the soluble transhydrogenases (sTH) or alternative mechanisms to balance NADPH levels in all other species. ${\mathrm{R}}_{\mathrm{U}}^{*}$ accounts for a currently unknown mechanism to balance NADPH levels in B. subtilis.

^§${\delta }^2$H values were calculated as ${\delta }^2$H = (${\mathrm{R}}_{\mathrm{e}\mathrm{n}\mathrm{z}\mathrm{y}\mathrm{m}\mathrm{e}}$/${\mathrm{R}}_{\mathrm{V}\mathrm{S}\mathrm{M}\mathrm{O}\mathrm{W}}$ − 1) $\times$ 1,000.

^¶Enrichment factors were estimated as $ϵ$ = ($\alpha$ − 1) $\times$ 1,000 and $ϵ$ = (${\delta }^2$H + 1)/(${\delta }^2{\mathrm{H}}_{\mathrm{w}\mathrm{a}\mathrm{t}\mathrm{e}\mathrm{r}}$ + 1) − 1.

^∥Enrichment factors are calculated from in vitro KIEs according to $ϵ$ = (1/KIE − 1) $\times$ 1,000.