Involvement of cytochrome b 5 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 Δ 6 ‐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 Δ 6 ‐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 b 5 and NADPH‐cytochrome c reductase, only the antibody against cytochrome b 5 demonstrated a marked ability to inhibit the Δ 6 ‐desaturase activity. This evidence supports a participation of cytochrome b 5 in the Δ 6 ‐desaturation of linoleic acid and suggests a pathway analogous to the Δ 9 ‐desaturation of stearyl‐CoA.