TABLE 2

Apparent kinetic parameters for morphine-3-glucuronide formation catalyzed by human liver microsomes

UGT activity was determined with 18 substrate concentrations up to 5 mM for pooled human liver microsomes (HLM) in the presence of 2 mM UDP-GlcA. For individual HLM, assays were performed with eight substrate concentrations up to 5 mM. Data were fit to the Michaelis-Menten equation. Numbers in parentheses represent the value normalized by the UGT2B7 content that was assumed by using baculovirus cell lysate containing recombinant UGT2B7 protein as the standard. Results are the estimated value ± S.D.

Cells KmVmaxVmax/Km
mM pmol / min / mg of protein
Pooled HLM 1.18 ± 0.21 274 ± 24 232
Individual HLM A 1.30 ± 0.12 409 ± 14 (330) 315 (253)
Individual HLM B 0.76 ± 0.18 432 ± 32 (507) 568 (667)
Individual HLM C 1.17 ± 0.13 360 ± 14 (330) 308 (282)