title: Further studies on the substrate spectrum of phytanoyl-CoA hydroxylase: implications for Refsum disease?
abstract: Refsum disease is a peroxisomal disorder characterized by adult-onset retinitis pigmentosa, anosmia, sensory neuropathy, ataxia, and an accumulation of phytanic acid in plasma and tissues. Approximately 45% of cases are caused by mutations in phytanoyl-CoA hydroxylase (PAHX), the enzyme catalyzing the second step in the peroxisomal alpha-oxidation of 3-methyl-branched fatty acids. To study the substrate specificity of human PAHX, different 3-alkyl-branched substrates were synthesized and incubated with a recombinant polyhistidine-tagged protein. The enzyme showed activity not only toward racemic phytanoyl-CoA and the isomers of 3-methylhexadecanoyl-CoA, but also toward a variety of other mono-branched 3-methylacyl-CoA esters with a chain length down to seven carbon atoms. Furthermore, PAHX hydroxylated a 3-ethylacyl-CoA quite well, whereas a 3-propylacyl-CoA was a poor substrate. Hydroxylation of neither 2- or 4-methyl-branched acyl-CoA esters, nor long or very long straight-chain acyl-CoA esters could be detected. The results presented in this paper show that the substrate specificity of PAHX, with regard to the length of both the acyl-chain and the branch at position 3, is broader than expected. Hence, Refsum disease might be characterized by an accumulation of not only phytanic acid but also other 3-alkyl-branched fatty acids.
authors.affiliation: Departement Moleculaire Celbiologie, Afdeling Farmacologie, Katholieke Universiteit Leuven, Campus Gasthuisberg, Herestraat 49, B-3000 Leuven, Belgium.
authors.forename: Veerle
authors.initials: V
authors.lastname: Foulon
authors.forename: Stanny
authors.initials: S
authors.lastname: Asselberghs
authors.forename: Wendy
authors.initials: W
authors.lastname: Geens
authors.forename: Guy P
authors.initials: GP
authors.lastname: Mannaerts
authors.forename: Minne
authors.initials: M
authors.lastname: Casteels
authors.forename: Paul P
authors.initials: PP
authors.lastname: Van Veldhoven
mesh_terms: D003065:Coenzyme A / Q000378:metabolism; D006801:Humans; D006900:Hydroxylation; D007700:Kinetics; D006899:Mixed Function Oxygenases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D015394:Molecular Structure; D010831:Phytanic Acid / Q000031:analogs & derivatives* / Q000378:metabolism; D012035:Refsum Disease / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*; D013329:Structure-Activity Relationship; D013379:Substrate Specificity
chemical_list: C089917:phytanoyl-coenzyme A; D010831:Phytanic Acid; D006899:Mixed Function Oxygenases; C102623:PHYH protein, human; D003065:Coenzyme A