Abstract
The different topology of palmitoyl-CoA ligase (on the cytoplasmic surface) and of lignoceroyl-CoA ligase (on the luminal surface) in peroxisomal membranes suggests that these fatty acids may be transported in different form through the peroxisomal membrane (Lazo, O., Contreras, M., and Singh, I. (1990) Biochemistry 29, 3981-3986), and this differential transport may account for deficient oxidation of lignoceric acid in X-adrenoleukodystrophy (X-ALD) (Singh, I., Moser, A. B., Goldfisher, S., and Moser, H. W. (1984) Proc. Natl. Acad. Sci. U.S.A. 81, 4203-4207). To define the transport mechanism for these fatty acids through the peroxisomal membrane and its possible implication to lignoceric acid metabolism in X-ALD, we examined cofactors and energy requirements for the transport of palmitic and lignoceric acids in isolated peroxisomes from rat liver and peroxisomes isolated from X-ALD and control fibroblasts. The similar rates of transport of palmitoyl-CoA (87.6 +/- 6.3 nmol/h/mg protein) and palmitic acid in the fatty acid activating conditions (83.4 +/- 5.1 nmol/h/mg protein) and lack of transport of palmitic acid (4% of palmitoyl-CoA transport) when ATP and/or CoASH were removed or substituted by alpha,beta-methyleneadenosine-5'-triphosphate (AMPCPOP) and/or desulfoCoA-agarose from assay medium clearly demonstrate that transport of palmitic acid requires prior synthesis of palmitoyl-CoA by palmitoyl-CoA ligase on the cytoplasmic surface of peroxisomes. The 10-fold higher rate of transport of lignoceric acid (5.3 +/- 0.6 nmol/h/mg protein) as compared with lignoceroyl-CoA (0.41 +/- 0.11 nmol/h/mg protein) and lack of inhibition of transport of lignoceric acid when ATP and/or CoASH were removed or substituted with AMPCPOP or desulfoCoA-agarose suggest that lignoceric acid is transported through the peroxisomal membrane as such. Moreover, the lack of effect of removal of ATP or substitution with AMPOPCP (a nonhydrolyzable substrate) demonstrates that the translocation of palmitoyl-CoA and lignoceric acid across peroxisomal membrane does not require energy. The transport, activation, and oxidation of palmitic acid are normal in peroxisomes from X-ALD. The deficient lignoceroyl-CoA ligase (13% of control) and oxidation of lignoceric acid (10% of control) as compared with normal transport of lignoceric acid into peroxisomes from X-ALD clearly demonstrates that pathogenomonic accumulation of very long chain fatty acids (greater than C22) in X-ALD is due to the deficiency of peroxisomal lignoceroyl-CoA ligase activity.
Highlights
The different topology of palmitoyl-CoA ligase (on oxidation of lignoceric acid (10%of control) as comthe cytoplasmic surface)and of lignoceroyl-CoA ligase pared with normal transport of lignoceric acid into in peroxisomalmembranes peroxisomesfrom X-ALD clearly demonstrates that suggests that these fatty acidsmay be transported in pathognomonic accumulation of very long chain fatty differentformthroughtheperoxisomalmembrane acids (>C,) in X-ALD is due to thedeficiency of per
To define the transport mechanism for these fatty acids through the peroxisomal membrane and its possible implication to lignoceric acid metabolism in X-ALD, we examined cofactors and energy requirements for the transport of palmitic and lignoceric acids in isolated peroxisomes fromrat liver andperoxisomes isolated fromX-ALD and controlfibroblasts
Sine-5”triphosphate (AMPCPOP) and/or desulfoCoA- Palmitic acid (Cleo)and lignoceric acid (C,) in peroxisomal agarose from assay medium clearly demonstrate that membranes are activated by two different enzymes (10, l l ), transport of palmitic acid requires prior synthesis of palmitoyl-CoA by palmitoyl-CoA ligase on the cytoplasmic surface of peroxisomes
Summary
From the Departmentof Pediatrics, Medical University of South Carolina, Charleston, South Carolina 29425. Palmitoyl-CoA transport) when ATP and/or CoASH for p-oxidation the fattyacids are activated in the were removed or substituted by a,&methyleneadeno- peroxisomal membrane and p-oxidized in the matrix. The deand the active site of palmitoyl-CoA ligase is on the cytoplasmic surface of the peroxisomal membrane [2, 8] whereas the active site of the lignoceroyl-CoA ligase is on the luminal side of the peroxisomal membranes [8] suggesting possibly different mechanisms of transport of palmitic and lignoceric acids. This article than the deficient activity of lignoceroyl-CoA ligase To answer these questions, we examined the transportof palmitic acid and lignoceric acid into peroxisomes.
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