NADH-DEPENDENT AND NADPH-DEPENDENT DESATURATION OF LINOLEIC-ACID IN THE EXTRACTED MICROSOMAL FRACTION OF RAT-LIVER, AND RELATED EFFECTS OF CATALASE AND HYDROGEN-PEROXIDE

The NADPH-dependent Δ6 desaturation of linoleic acid is decreased by low ionic strength extraction of the microsomal fraction from rat liver. On the other hand, the NADH-dependent desaturase activity is slightly increased. Addition of the extract restores the NADPH-dependent Δ6 desaturase activity of the extracted microsomal fraction. Our results from gel filtration experiments on the extracted proteins show a correlation between the catalase activity of the eluate and the ability of the eluate to stimulate Δ6 desaturase activity. Both the NADH- and NADPH-dependent Δ6 desaturase activity of the extracted microsomal fraction are totally inhibited by exogenous hydrogen peroxide. The inhibitory effect of hydrogen peroxide is partly eliminated by addition of bovine catalase. Neither Superoxide dismutase, tert-butanol nor β-carotene stimulate the Δ6 desaturase activity of the extracted microsomal fraction. The Δ6 desaturase activity of the extracted microsomal fraction is decreased using NADH and NADPH simultaneously as electron donors. On the basis of these results we suggest that the decreased NADPH-dependent desaturase activity of the extracted microsomal fraction is due to a microsomal formation of hydrogen peroxide which possibly inactivates one or more components of the microsomal electron transport system. Furthermore, in the present microsomal fraction the formation of hydrogen peroxide seems to be NADPH-dependent. © 1979.