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Oxidation of 3‐oxygenated Δ 4 ‐ and Δ 5 ‐C 27 steroids by soybean lipoxygenase and rat liver microsomessteroids by soybean lipoxygenase and rat liver microsomes
Author(s) -
Aringer Leif
Publication year - 1980
Publication title -
lipids
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.601
H-Index - 120
eISSN - 1558-9307
pISSN - 0024-4201
DOI - 10.1007/bf02534180
Subject(s) - microsome , lipoxygenase , microsoma , biochemistry , enzyme , chemistry , clinical chemistry , substrate (aquarium) , biology , medicine , endocrinology , ecology
The formation of dioxygenated metabolites of cholesterol, epicholesterol (5‐cholesten‐3α‐ol) 4‐cholesten‐3β‐ol, 4‐cholesten‐3α‐ol, 4‐cholesten‐3‐one and 4‐stigmasten‐3‐one was studied after incubations with soybean lipoxygenase and linoleic acid. From cholesterol and epicholesterol were formed the 7α‐hydroxy‐, 7α‐hydroperoxy‐, 7β‐hydroxy‐, 7β‐hydroperoxy‐, 7‐oxo and 5,6‐epoxyderivatives as well as 6β‐hydroxy‐4‐cholesten‐3‐one. All Δ 4 ‐steroids were hydroxylated in the 6α‐ and 6β‐positions. The ratios between the yields of 6β‐ and 6α‐hydroxylated metabolites varied between 3∶1 and 2∶1. Incubations with 4‐cholesten‐3α‐ol and 4‐cholesten‐3β‐ol also afforded the 4,5‐epoxides of these steroids. The ratios between the yields of the 4β,5β‐ and 4α,5α‐epoxides were ca. 4∶1 for 4‐cholesten 3β‐ol and ca. 3∶2 for 4‐cholesten‐3α‐ol. With iron‐supplemented microsomes from rat liver, the compounds formed were qualitatively and quantitatively the same as with soybean lipoxygenase, whereas with 18,000 × g rat liver supernatant fractions the yields of all products formed—except 7α‐hydroxycholesterol and 6β‐hydroxy‐4‐cholesten‐3‐one—were markedly decreased. The results indicate the presence of a rat liver microsomal 6β‐hydroxylase which can use 4‐cholesten‐3‐one as a substrate and extend previous findings of similarities between soybean lipoxygenase and a nonspecific lipoxygenase in rat liver microsomes.