Involvement of cytochrome b5 in the oxidative desaturation of linoleic acid to γ-linolenic acid in rat liver microsomes

The effects of antibodies against microsomal electron-transport components on the in vitro activity of Δ⁶-desaturation of linoleic acid to γ-linolenic acid have been studied in intact microsomal membranes of rat liver. Reduced nicotinamide adenine dinucleotide (NADH) or reduced nicotinamide adenine dinucleotide phosphate (NADPH) (0.87 mM) served as electron donors, and effectively prompted the Δ⁶-desaturase activities with yields of about 1.1 to 1.3 nmol per mg of protein in 10 min. Of the two antibodies studied under the same in vitro conditions, i.e., rabbit antisera preparations against rat liver microsomal hydrophilic parts of cytochrome b₅ and NADPH-cytochrome c reductase, only the antibody against cytochrome b₅ demonstrated a marked ability to inhibit the Δ⁶-desaturase activity. This evidence supports a participation of cytochrome b₅ in the Δ⁶-desaturation of linoleic acid and suggests a pathway analogous to the Δ⁹-desaturation of stearyl-CoA.