Table 2

Kinetic parameters of glucuronide formation in a membrane preparation from HK 293 cells stably expressing UGT2B7(Y)

SubstrateApparentKM VmaxVmax/KM
mM pmol/min/mg μl/min/mg (× 100)
 3-OH position1.030931
 6-OH position1.3473.6

Rates were measured using a single membrane preparation from cells after 3–4 passages. Assays were conducted as described inMaterials and Methods at established optimum conditions for each substrate and 2 mM UDP-GlcUA. Formation of morphine-3-, morphine-6-, and codeine glucuronides was analyzed by the HPLC method, whereas formation of nalorphine and buprenorphine glucuronide was established using the extraction method of Puig and Tephly (9). Data represent the mean values obtained from two different determinations.