Table 1.

Concentrations and parameters of substrates and cholinesterases

	Substratea(µM)	AChEb(µM)	BChEb(µM)	Km (µM)	Vmax (µmol·min−1·L−1)	Vmax/Km (min−1)	First-order ratec(min−1)
MP4A	17	0.00022 (0.015)	–	1600 ± 90	31 ± 0.58	0.019	0.019 ± 0.00038
MP3B_R	17	–	0.0014 (0.32)	260 ± 4.9	20 ± 0.099	0.077	0.080 ± 0.0024

^aThe substrate concentrations shown were obtained using 10 µL of solution containing 4 kBq of radiolabelled substrate (2.0 MBq·µmol⁻¹) to 100 µL of enzyme solution.

^bThe concentrations of AChE (84 U·L⁻¹) and BChE (33 U·L⁻¹) used for parameter estimation were calculated using reported turn-over numbers (k_cat: AChE, 390 000·min⁻¹; BChE, 24 000·min⁻¹) (Blong et al., 1997; Cohen et al., 2001). In addition, the concentrations of the cholinesterases in the human whole blood were calculated based on the reported AChE and BChE activities (AChE: 19 U·L⁻¹; BChE: 24 U·L⁻¹) measured with ATCh and BTCh, respectively, in 316-fold diluted human whole blood at 37°C (Worek et al., 1999), and are presented in parentheses.

^cThe first-order hydrolysis rates of substrates in the human pure enzyme solution used for parameter estimation are presented as mean ± SEM of triplicate values.