Behavior of Unsaturated Fatty Acids in the Thiobarbituric Acid Test after Radiolysis

Abstract

The thiobarbituric acid (TBA) test is often employed as an index of the extent of oxidation of the naturally occurring highly unsaturated fatty acids. Various colorimetric procedures exist in which lipid-containing mixtures are heated with TBA. Appearance of a pink chromogen having an absorption maximum at about 532 mji is characteristic for oxidation products of highly unsaturated fatty acids. Wilbur et al. observed that TBA-active products are obtained by ultraviolet irradiation of unsaturated fatty acids in air (1). The TBA-active products were also obtained by irradiation of the skin of mice. Subsequently, the TBA test has been frequently employed in attempts to assess the oxidation status of unsaturated fatty acids after exposure to diverse radiation. Whole-body X-irradiation of rabbits resulted in an increased TBA activity of bone marrow (2). Intestinal mucosa, removed from rats after whole-body X-irradiation, was observed to promote oxidation of both a suspension of methyl linolenate and a homogenate of liver as evidenced by a pronounced response in a TBA test (3). Ultraviolet irradiation of mitochondrial suspensions resulted in oxidation of unsaturated fatty acids as observed with a TBA test (4). A concomitant loss of succinoxidase and choline oxidase activities occurred which paralleled the intensity of color in the TBA test. Inhibition of succinoxidase of nonirradiated mitochondria could also be produced by incubation with TBA-active products obtained from ultraviolet-irradiated methyl linolenate. The degree of inhibition did not depend on whether endogenous or exogenous lipid was oxidized, but was related to the level of TBA-active products. Extracts of ultraviolet-irradiated methyl linolenate, having high TBA activity, inhibited respiration in yeast cells (5) and also inhibited