Mitochondrial and Peroxisomal β‐Oxidation of Stearic and Lignoceric Acids by Rat Brain

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Abstract
Crude subcellular fractions were prepared from adult rat brains by differential centrifugation of brain ho‐mogenates. Greater than 98% of the cellular mitochondrial marker enzyme activity sedimented in the heavy and light mitochondrial pellets, and <1% of the activity sedimented in microsomal pellets. Lysosomal marker enzyme activities mainly (71‐78% of cellular activity) sedimented in the heavy and light mitochondrial pellets. Significant amounts of the lysosomal marker enzyme activity also sedimented in the crude microsomal pellets (9‐13% of total) and high‐speed supernatants (14‐16% of total). The specific activities of microsomal and peroxisomal marker enzyme activities were highest in the crude microsomal pellets. Fractionation of the crude microsomal pellets on Nycodenz gradients resulted in the separation of the bulk of the remaining mitochondrial, lysosomal, and microsomal enzyme activities from peroxisomes. Fatty acyl‐CoA synthetase activities separated on Nycodenz gradients as two distinct peaks, and the minor peak of the activities was in the peroxisomal enriched fraction. Fatty acid β‐oxidation activities also separated as two distinct peaks, and the activities were highest in the peroxisomal enriched fractions. Mitochondria were purified from the heavy mitochondrial pellets by Percoll density gradients. Fatty acyl‐CoA synthetase and fatty acid β‐oxidation activities were present in both the purified mitochondrial and peroxisomal enriched fractions. Stearoyl‐CoA synthetase activities were severalfold greater compared to lignoceroyl‐CoA synthetase, and stearic acid β‐oxidation was severalfold greater compared to lignoceric acid β‐oxidation in purified mitochondrial and peroxisomal enriched fractions. The results presented demonstrate conclusively that, in contrast to rat liver and human skin fibroblasts, rat brain mitochondria contain lignoceroyl‐CoA synthetase, as well as lignoceric acid β‐oxidation activities

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