Human placental glutathione S-transferase-mediated metabolism of methyl parathion

The ability of human placental glutathione S-transferase (GSHTr) to metabolize methyl parathion (MeP) was examined. MeP was found to be a substrate for both partially purified pre-term and highly purified term placental GSHTr. The characterization of the reaction by high performance liquid chromatography revealed the presence of desmethyl parathion (DesMeP) as the sole metabolite. Term placental GSHTr activity towards MeP ranged from 2.22 to 3.53 nmoles DesMeP formed X min-1 X mg-1 while an activity of 0.60 to 1.12 nmoles DesMeP formed X min-1 X mg-1 was observed with the pre-term placental enzyme. The absence of the O-dearylation reaction by pre-term and term placental GSHTr represents a major species- and/or tissue-specific difference.