Comparative effect of a protein diet on the desaturation,elongation and simultaneous desaturation and elongation of linoleic acid

The effect of a protein diet on the biosynthesis of polyunsaturated fatty acids of the linoleic acid family was studied by incubation of rat liver microsomes with labeled linoleic acid. The incubation was performed in desaturating, elongating and desaturating-elongating conditions. In desaturating conditions, linoleic acid was converted to γ-linolenic acid, whereas in elongating conditions it was converted to 20∶2, 22∶2 and 24∶2. In desaturating-elongating conditions, labeling was found in γ 18∶3, 20∶2, 20∶3, 20∶4 and 22∶2. A protein diet increased the oxidative desaturation of linoleic acid to γ-linolenic and arachidonic acid biosynthesis, whereas the elongating reaction was not enhanced in the experimental conditions tested. It is suggested that the main controllable step in the linoleic acid family is the oxidative desaturation of linoleic acid to γ-linolenic acid.