5α,6α-Epoxy-cholestan-3β-ol (cholesterol α-oxide): A specific substrate for rat liver glutathione transferase B |
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Authors: | David J Meyer Brian Ketterer |
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Institution: | Courtauld Institute of Biochemistry, Middlesex Hospital Medical School, London W1P 7PN, England |
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Abstract: | A semi-micro assay was developed for the conjugation of 5α,6α-epoxy-cholestan-3β-ol (cholesterol α-oxide) with glutathione. The soluble supernatant of rat liver homogenate catalysed the reaction at a rate of 0.2–0.5 pmol.min−1 .mg protein−1 with 4μM cholesterol α-oxide, while the reaction in the presence of GSH alone was barely detectable. Enzymic activity in the soluble supernatant was due equally to the two forms of glutathione transferase B (100 pmol.min−.mg protein−1), glutathione transferases AA, A, C and E being unreactive. The activity of purified glutathione transferase B was about 5-times that expected from the activity of the soluble supernatant. Complex enzyme kinetics were obtained suggestive of substrate inhibition. |
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Keywords: | Glutathione transferase B Cholesterol α -oxide substrate |
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