Table 3.
Kinetic parameters of the steps mediating the de novo biosynthesis of PC from exogenous choline (erythrocyte and parasite choline carrier and Kennedy pathway enzymes) and inhibitory effect of albitiazolium
| Transporter/enzyme | Erythrocyte choline entry | Parasite choline entry | CK | CCT | CEPT |
|---|---|---|---|---|---|
| Km (µM) | 11.0 ± 2.4 | 18.5 ± 3.3 | 31.2 ± 4.1 | 511.0 ± 24.8 | 13.2 ± 0.7 |
| Vmax (pmol per 107 IRBC·min−1) | 0.7 ± 0.2 | 23.3 ± 4.5 | 63.3 ± 11.6 | 5.2 ± 1.4 | 17.0 ± 1.5 |
| IC50 of albitiazolium (µM) | 2.9 ± 0.8* | 2.3 ± 0.2 | 1500 | 2500 | 4200 |
Choline entry into infected erythrocytes and parasites followed Michaelis–Menten kinetics. Inhibitory effect of albitiazolium on each step is expressed as IC50 and measured when choline (transporter) or the choline-containing metabolites (enzymes) were close to their apparent respective Km (i.e. one to twofold their respective Km).
For the endogenous choline carrier, inhibition was achieved in the presence of 150 µM furosemide to inhibit choline entry by furosemide-sensitive NPP.
Values are means of at least three independent experiments performed in duplicate (SEM is indicated). Otherwise, values are means of two independent experiments.