Conversion of sterols and triterpenes by mycobacteria. II. Transformation of 7-oxygenated sterols into androstane derivatives via a 7-deoxygenation.
The bioconversion of 7-oxygenated sterols by Mycobacterium aurum was studied in a preliminary investigation of the microbial conversion of wool wax. 7-Oxocholesterol was found to be transformed mainly into 3,17-dioxygenated androstane derivatives. 7 xi-Hydroxylated sterols were formed in an initial reduction step, and the C-7 hydroxyl group was then eliminated in a dehydration reaction. This was thought to take place during the isomerisation of cholest-4-en-3-one to cholest-5-en-3-one. Deuterium labelling experiments showed that this elimination proceeded faster for the C-7 alpha isomer, although it was not stereospecific. The C-7 alpha and C-7 beta-hydroxy isomers were weakly interconverted via the 7-oxo derivatives. Cholest-4-en-3-one, cholest-1,4-dien-3-one and cholest-4,6-dien-3-one all lost their side chains following a hydrogenation/dehydrogenation reaction. The resulting 3,17-dioxoandrostene or 3,17-androstadiene derivatives were mainly hydrogenated into 5 alpha-androstane-3,17-dione and 5 alpha-androstane-3 beta-ol-17-one. Elimination of the 3 beta-hydroxyl groups giving cholesta-3,5-dien-7-one, and subsequent microbial degradation of the side chain was not observed to any significant extent. The convergence of the bioconversion pathways of cholesterol and the 7-oxygenated cholesterols enabled crude, partially auto-oxidised cholesterol to be used as a substrate for the production of 3,17-dioxygenated androstane derivatives by M. aurum.
Prome
D
D
Centre de Recherche de Biochimie et Génétique Cellulaires C.N.R.S., Toulouse, France.
Clave
C
C
Escoffier
B
B
Prome
J C
JC
D000731:Androstanes / Q000096:biosynthesis*; D001711:Biotransformation; D002784:Cholesterol / Q000031:analogs & derivatives*; D008401:Gas Chromatography-Mass Spectrometry; D007536:Isomerism; D007653:Ketocholesterols / Q000378:metabolism*; D009161:Mycobacterium / Q000378:metabolism*; D010084:Oxidation-Reduction
D000731:Androstanes; D007653:Ketocholesterols; D002784:Cholesterol; C003001:7-ketocholesterol