Table 1.

Steady-state kinetic constants of cytidylyltransferases^a

Enzyme	Substrate	kcat (s−1)	KM (mM)	kcat/KM (M−1 s−1)	Specificityb	Ref.
Ari-PntC	AEP	3.7 ± 0.1	0.012 ± 0.001	3.2 × 105	0.0023	This work
	ChoPc	0.7 ± 0.3	1.0 ± 0.8	7.2 × 102
Spn-LicC	AEP	0.72 ± 0.05	0.3 ± 0.1	2.3 × 103	200	This work
	ChoPd	1.06 ± 0.04	2.4( ± 0.6)x10−3	4.5 × 105
	ChoP	3.6	0.060	6.0 × 104	2700	30
	PEtn	0.031	1.43	22
	ChoP	17.5	0.39	4.5 × 104		29
	ChoP	37	0.066	5.6 × 105		26
Tde-PntC	AEP	1.05 ± 0.05	0.016 ± 0.005	6.8 × 104	ND	This work
	ChoP	NDe	ND	ND

PEtn phosphoethanolamine

^aStandard errors are included for data generated in this work

^bRatio of specificity constants (k_cat/K_M) for ChoP:AEP (or PEtn)

^cSubstrate inhibition observed with K_S = 4 ± 1 mM

^dSubstrate inhibition observed with K_S = 6.4 ± 0.9 mM

^eND, not determined due to low activity