Abstract
Abstract Previous studies have shown that the major pathway for degradation of phytanic acid (3,7,11,15-tetramethylhexadecanoic acid) in rat liver and human skin fibroblasts involves an initial α decarboxylation. Identification of a series of homologous catabolic products led to the postulation of a pathway continuing via successive subsequent β oxidations. This would be expected to yield propionate fragments at the points of methyl substitution. In the present studies, [14C]propionate was characterized and quantified as a transient intermediate accumulating during degradation of [U-14C]phytanate in a particulate fraction of rat liver. Definitive demonstration of propionate as a major product was obtained using mutant lines of human fibroblasts from patients with inherited disorders blocking propionate oxidation (propionic acidemia and methylmalonic acidemia). Up to 5% of the added [U-14C]phytanate accumulated as [14C]propionate or [14C]methylmalonate in such cultures, actually exceeding the yield of 14CO2. Little or no propionate accumulated when [1-14C]palmitate was added as substrate excluding resynthesis. This evidence for direct generation of propionate from phytanate strongly supports the pathway involving α oxidation followed by successive classical β oxidation.
Highlights
Identification of a series of homologous catabolic products led to the postulation of a pathway continuing via successive subsequent /3 oxidations
Studies in Rat Liver-Livers from normal male SpragueDawley rats were homogenized with glass homogenizers in 0.01 RZ
The degradation of phytanic acid (3,7,11,15-tetramethglhexadecanoic acid) is believed to involve an initial QI oxidative decnrhosylat~ion, yielding prist.anic acid, followctl by successive /3 osidative cleavages with alternate release of CB and Cr fragments (Fig. 1) (I-4). cyHytlrorylat,ion has been demonstrat.etl directly [4] and a series of expected homologous degradation products has been identified by combined gas-liquid chromatography and mass spectrometry
Summary
Identification of a series of homologous catabolic products led to the postulation of a pathway continuing via successive subsequent /3 oxidations This would be expected to yield propionate fragments at the points of methyl substitution. Little or no propionate accumulated when [l-14C]pahnitate was added as substrate excluding resynthesis This evidence for direct generation of propionate from phytanate strongly supports the pathway involving Q! Degradation from the w end by successive /3 oxidations would yield propionate fra.gments, as in the case of the pathway proposed, and generate a series of homologous dicarboxylic acids.
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