Table 1

Kinetic parameters (K_m and V_max) forO-methylation of increasing concentrations of (−)-epicatechin and (−)-epigallocatechin by human placental cytosolic preparations

Placenta	(−)-Epicatechin		(−)-Epigallocatechin
Placenta	K_m	V_max	V_max/K_m	K_m	V_max	V_max/K_m
	μM	pmol/mg protein/min		μM	pmol/mg protein/min
NP5C	2.2	495	225.0
NP10C	6.2	257	41.5
NP12C	8.2	225	27.4
NP13C	8.2	311	37.9	4.8	193	40.2
NP18C	6.7	310	46.3	3.9	310	79.5
NP21C	9.1	189	20.8	6.7	207	30.9

The incubation mixture consisted of (−)-epicatechin (0, 5, 10, 20, 30, 40, and 50 μM) or (−)-epigallocatechin (0, 1, 2, 4, 8, 12, 16, and 20 μM), 25 μMS-[methyl-³H]adenosyl-l-methionine (0.2 μCi), 1.0 mg/ml placental cytosolic protein, 1 mM dithiothreitol, and 1.2 mM MgCl₂ in a final volume of 1.0 ml of Tris-HCl buffer (10 mM, pH 7.4). The incubations were carried out at 37°C for 20 min. Each point is the mean of duplicate determinations.