TY - JOUR
T1 - Radiometric assays for mammalian epoxide hydrolases and glutathione S-transferase
AU - Gill, Sarjeet S.
AU - Ota, Kenji
AU - Hammock, Bruce D.
PY - 1983
Y1 - 1983
N2 - A number of epoxides, including cis- and trans-stilbene oxides, were assayed as substrates for epoxide hydrolases (EHs) by gas-liquid chromatography. Radiolabeled stilbene oxides were prepared by sodium borotritide reduction of desyl chloride followed by ring closure with base treatment. Rapid radiometric assays for EHs were performed by differential partitioning of the epoxide into dodecane, while the product diol remained in the aqueous phase. Glutathione (GSH) transferase was similarly assayed by partitioning the epoxide and diol, if formed metabolically, into 1-hexanol, while the GSH conjugate was retained in the aqueous phase. The cytosolic EH rapidly hydrates the trans isomer while the cis is very poorly hydrated. In contrast, the cis is a better substrate for the microsomal EH than the trans. GSH transferase utilized both epoxides as substrates, but conjugation is faster with the cis isomer. Cytosolic EH activity is high in mouse but very low in rat and guinea pig. Microsomal EH activity, in contrast, is highest in guinea pig, intermediate in rat, and the lowest in mouse. GSH transferase activity, which is high in all three species, can be inhibited by chalcone, with an I50 of 3.1 × 10-5 m. These assays facilitate the rapid evaluation and direct comparison of epoxide-metabolizing systems in cell homogenates used in short-term mutagenicity assays, cell or organ culture, and possibly in vivo.
AB - A number of epoxides, including cis- and trans-stilbene oxides, were assayed as substrates for epoxide hydrolases (EHs) by gas-liquid chromatography. Radiolabeled stilbene oxides were prepared by sodium borotritide reduction of desyl chloride followed by ring closure with base treatment. Rapid radiometric assays for EHs were performed by differential partitioning of the epoxide into dodecane, while the product diol remained in the aqueous phase. Glutathione (GSH) transferase was similarly assayed by partitioning the epoxide and diol, if formed metabolically, into 1-hexanol, while the GSH conjugate was retained in the aqueous phase. The cytosolic EH rapidly hydrates the trans isomer while the cis is very poorly hydrated. In contrast, the cis is a better substrate for the microsomal EH than the trans. GSH transferase utilized both epoxides as substrates, but conjugation is faster with the cis isomer. Cytosolic EH activity is high in mouse but very low in rat and guinea pig. Microsomal EH activity, in contrast, is highest in guinea pig, intermediate in rat, and the lowest in mouse. GSH transferase activity, which is high in all three species, can be inhibited by chalcone, with an I50 of 3.1 × 10-5 m. These assays facilitate the rapid evaluation and direct comparison of epoxide-metabolizing systems in cell homogenates used in short-term mutagenicity assays, cell or organ culture, and possibly in vivo.
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U2 - 10.1016/0003-2697(83)90166-5
DO - 10.1016/0003-2697(83)90166-5
M3 - Article
C2 - 6614459
AN - SCOPUS:0020620574
VL - 131
SP - 273
EP - 282
JO - Analytical Biochemistry
JF - Analytical Biochemistry
SN - 0003-2697
IS - 1
ER -