Table 3

Michaelis-Menten constants for zero-trans influx of nucleosides in ARAC/D2 and CEM cells

Nucleoside	ARAC/D2		CEM
Nucleoside	K_m	V_max	V_max/K_m	K_m	V_max	V_max/K_m
	μM	pmol/μl cell water/s			pmol/μl cell water/s
Uridine	46 ± 4	0.42 ± 0.05	0.009	192 ± 10	27 ± 11	0.14
5-Fluorouridine	43 ± 7	0.38 ± 0.07	0.009	217 ± 16	22 ± 9	0.10

Initial rates of uptake were determined for each of the graded concentrations of [³H]uridine (ARAC/D2, 0–100 μM; CEM, 0–400 μM) or [³H]5-fluorouridine (ARAC/D2, 0–100 μM; CEM, 0–400 μM). The K _m andV _max values are the means ± S.D. of individual values determined from Woolf, Eadie-Hofstee, and Lineweaver-Burke plots for each of the three independent experiments. Uridine and 5-fluorouridine were not transported by CEM-ARAC cells (data not shown).

3-a Expressed as μM.