Stereochemistry of the alpha-oxidation of 3-methyl-branched fatty acids in rat liver.
The stereochemistry of the alpha-oxidation of 3-methyl-branched fatty acids was studied in rat liver. R- and S-3-methylhexadecanoic acid were equally well alpha-oxidized in intact hepatocytes and homogenates. Subcellular fractionation studies showed that alpha-oxidation of both isomers is confined to peroxisomes. Dehydrogenation of 2-methylpentadecanal, the end-product of the peroxisomal alpha-oxidation of 3-methylhexadecanoic acid, to 2-methylpentadecanoic acid, followed by derivatization with R-1-phenylethylamine and subsequent separation of the stereoisomers by gas chromatography, revealed that the configuration of the methyl-branch is preserved throughout the whole alpha-oxidation process. Metabolism and formation of the 2-hydroxy-3-methylhexadecanoyl-CoA intermediate were also investigated. Separation of the methyl esters of the four isomers of 2-hydroxy-3-methylhexadecanoic acid was achieved by gas chromatography after derivatization of the hydroxy group with R-2-methoxy-2-trifluoromethylphenylacetic acid chloride and the absolute configuration of the four isomers was determined. Although purified peroxisomes are capable of metabolizing all four isomers of 2-hydroxy-3-methylhexadecanoyl-CoA, they can only form the (2S,3R) and the (2R,3S) isomers. Our experiments exclude the racemization of the 3-methyl branch during the alpha-oxidation process. The configuration of the 3-methyl branch does not influence the rate of alpha-oxidation, but determines the side of the 2-hydroxylation, hence the configuration of the 2-hydroxy-3-methylacyl-CoA intermediates formed during the process.
Croes
K
K
Katholieke Universiteit Leuven, Campus Gasthuisberg, Departement Moleculaire Celbiologie, Afdeling Farmacologie, Herestraat 49, B-3000 Leuven, Belgium.
Casteels
M
M
Dieuaide-Noubhani
M
M
Mannaerts
G P
GP
Van Veldhoven
P P
PP
D000818:Animals; D002458:Cell Fractionation; D002849:Chromatography, Gas; D006900:Hydroxylation; D007700:Kinetics; D008099:Liver / Q000737:chemistry* / Q000648:ultrastructure; D008297:Male; D008830:Microbodies / Q000378:metabolism; D010084:Oxidation-Reduction; D010169:Palmitic Acids / Q000737:chemistry* / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D013237:Stereoisomerism
D010169:Palmitic Acids; C034840:3-methylhexadecanoic acid