Table 1.

Comparison of kinetic parameters of the enzymes involved in the last two steps of NAD synthesis in F. tularensis and B. anthracis

Protein, substrateKinetic constants
kcat/Km, s−1·M−1Subs. pref., fold
kcat, s−1Km, mM
Amidation step
    ftNadE*, NaMN0.50 ± 0.020.20 ± 0.042,500≈60
    ftNadE*, NaAD0.25 ± 0.025.82 ± 1.1343
    baNadE, NaMN0.004 ± 0.00021.18 ± 0.173≈3,000
    baNadE, NaAD2.64 ± 0.060.29 ± 0.029,100
Adenylylation step
    ftNadM, NaMN0.16 ± 0.010.81 ± 0.27200≈400§
    ftNadM, NMN2.8 ± 0.10.034 ± 0.00482,000
    baNadD, NaMN25.60 ± 1.20.04 ± 0.01640,000≈45,000
    baNadD, NMN0.014 ± 0.0010.94 ± 0.1215
  • The apparent values of Km (mM) and kcat (s−1) of ftNadE* and baNadE enzymes for amidation of both alternative substrates, NaMN and NaAD, at saturating concentrations of ATP (2 mM) and NH4Cl (4 mM), and of baNadD and ftNadM enzymes for adenylylation of NaMN and NMN at saturating concentration of ATP (2 mM) were determined as described in SI Appendix, SI Text. Errors represent standard deviation. Substrate preference (Subs. pref.) is expressed as a ratio of catalytic efficiencies (kcatapp/Kmapp) for the respective alternative substrates (see SI Appendix, SI Fig. 5 for kinetic rate plots).

  • NaMN > NaAD;

  • NaAD > NaMN;

  • §NMN > NaMN;

  • NaMN > NMN.