Palmitoyl-CoA Elongation in Brain Microsomes: Dependence on Cytochrome b5and NADH-Cytochrome b5Reductase

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Abstract
Experiments were performed to demonstrate the involvement of electron transport system in fatty acid elongation in rat brain microsomes. Mercuric chloride and p-chloromercuriphenylsulfonate, inhibitors on NADH-cytochrome b5 reductase, at 32 .mu.M inhibited NADH-supported palmitoyl-coA elongation to 30 and 60% of control activity, respectively, whereas NADPH-supported palmitoyl-CoA elongation was unaffected by these mercurials. An antibody to rat liver NADH-cytochrome b5 reductase inhibited brain microsomal NADH-cytochrome b5 reductase activity and NADH-dependent palmitoyl-CoA elongation. Treatment of brain microsomes with trypsin diminished the cytochrome b5 content: NADH- and NADPH-cytochrome c reductase activities were significantly decreased, but the decrease in NADH-cytochrome b5 reductase activity was relatively small. Whereas essentially no incorporation of malonylCoA into palmitoyl-coA was observed with trypsin-treated microsomes, addition of detergent-solubilized cytochrome b5 resulted in a recovery of fatty acid elongation. These results indicate the presence of an electron transport system, NADH-NADH-cytochrome b5 reductase-cytochrome b5-fatty acid elongation, in brain microsomes.

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