Open AccessStereochemistry of C‐1, 2‐Dehydrogenation during Cholesterol Degradation by Mycobacterium phlei
Author(s) -
Phillips Gareth T.,
Ross Frederick P.
Publication year - 1974
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1974.tb03517.x
Subject(s) - mycobacterium phlei , squalene , tritium , dehydrogenation , chemistry , stereospecificity , cholesterol , mevalonic acid , stereochemistry , organic chemistry , enzyme , biosynthesis , biochemistry , bacteria , mycobacterium , catalysis , biology , genetics , physics , nuclear physics
1 Cholesterol and squalene were synthesised, using rat liver enzymes, from (A) a mixture of [2 R ,3 R ‐2‐ 3 H 1 + 2 S ,3 S ‐2‐ 3 H 1 ] and (3 RS )‐[2‐ 14 C]mevalonate and (B) a mixture of [2 S ,3 R ‐2‐ 3 H 1 +2 R ,3 S ‐2‐ 3 H 1 ] and (3 RS )[2‐ 14 C]mevalonate. 2 The tritium labelling at position 1β of cholesterol synthesised from mixture (A) was calculated from the loss of tritium incurred during the oxidation of cholesterol to 7‐oxocholesteryl acetate. 3 Cholesterol labelled specifically at the 2β‐position was obtained from (C) a mixture of (3 RS , 5 S )[5‐ 3 H 1 ] and (3 RS )[2‐ 14 C]mevalonate in a rat liver preparation. The stereochemical purity of the mevalonate was verified from the tritium content of the squalene and of the cholesterol, and from the exchange of tritium from androsta‐1,4‐diene‐3,17‐dione obtained as a degradation product of cholesterol by Mycobacterium phlei.4 The three samples of cholesterol were transformed into androsta‐1,4‐diene‐3,17‐dione by cultures of M. phlei. The dehydrogenation proceeded with complete loss of tritium from the 1α and 2β‐positions. Tritium at the 1β‐position was completely retained. 5 In summary, the stereochemistry of the C‐1, 2‐dehydrogenation associated with the degradation of cholesterol to androsta‐1,4‐diene‐3,17‐dione by M. phlei proceeds via the stereospecific 1α,2β‐ trans ‐diaxial removal of hydrogen, and is similar to the stereochemistry of the C‐1,2‐dehydrogenation of analogous substrates with other bacteria mentioned in the text.