Raúl O. Peluffo

Regulation of unsaturated fatty acids biosynthesis 1. Effect of unsaturated fatty acid of 18 carbons on the microsomal desaturation of linoleic acid into γ-linolenic acid

Abstract 1. (1) [1- 14 C]Linoleic acid is desaturated by the microsomes of rat liver to γ-[1- 14 C]linolenic acid, and this reaction is inhibited by CN − . 2. (2) The addition of α-linolenic acid or of several monoenoic acids, such as oleic, petroselinic, vaccenic and elaidic acids, provoked an inhibition. 3. (3) Unlabeled cis -linoleic and γ-linolenic acids increase the desaturation, whereas all- trans -linoleic acid decreased the conversion of [1- 14 C]linoleic acid into yγ-linolenic acid. 4. (4) The activating effect evoked by cis -linoleic and γ-linolenic acids disappeared on the addition of heated microsomes or lysolecithin, so this activating effect may be the result of a competition between the transacylating and desaturating enzymes present in the microsomes when a small amount of labeled acid is incubated. 5. (5) When the concentration ratio of [1- 14 C]linoleic acid to microsomal protein was increased so that the desaturating enzyme was the limiting factor, cis -linoleic, trans -linoleic and γ-linolenic acids all inhibited linoleic acid desaturation. 6. (6) The desaturation of oleic, linoleic and α-linolenic acids may be regulated by competitive reactions among the three acids, other acids, their reaction products or by feed-back inhibition. The transacylating reaction may also modify the desaturation. Insulin and dietary conditions may induce an increase of desaturating enzyme activity.

Effect of insulin on the oxidative desaturation ofa-linolenic, oleic and palmitic acids

high-density lipoproteins were apparently the predominant species in the sera of chicken, rabbit, and mouse, the serum tipoprotein patterns of these species were similar to the human rather than to the rat. In all species except rat, when 3.75% gel was used, there was an absence of major lipoprotein components of mobilities intermediate to those of LDL and HDL. Other data indicate that a significant portion of the intermediate components observed with rat serum is probably attributable to the HDL~ (d = 1.050) fraction (2). Therefore the HDL1 fraction may be absent or present at low concentration in the sera of other species. Alternatively the characteristics of the serum HDL~ fraction may vary among species. A C K N O W L E D G M E N T S Blood samples provided by C. H. Walton, E. P. Royal, A. H. Sakr, and H. L. Creiniu. This work was supported by Career Development Award 5-K3-CA-31,063-02 and Research Grant CA4)1932-14 from the National Cancer Institute, U. S. Public Health Service. K . A N A N T H NARAYAN Burnsides Research L a b o r a t o r y University of Illinois Urbana, Illinois

Effect of different diets on the Δ9-desaturase activity of normal and diabetic rats

Abstract 1. (1) The in vivo Δ9-desaturase activity was measured in normal and diabetic rats by the intraperitoneal injection of [ 14 C]stearic acid and sodium [ 3 H]acetate. 2. (2) Dietary fructose, glycerol or saturated fatty acids were able to partially restore the Δ9-desaturase activity depressed by the diabetic state and to increase the activity of the enzyme in normal rats. 3. (3) The in vivo Δ9-desaturation activity was apparently induced by the increase in the endogenous or exogenous supply of saturated fatty acids. 4. (4) The different supplemented diets also increased the activity of the enzyme in liver microsomes of normal and diabetic rats. 5. (5) The increase in the saturated fatty acid synthesis by dietary fructose, glycerol or the exogenous supply of saturated fatty acids would result in an increase in the monounsaturated fatty acid synthesis via adaptive enzyme forma formation.

Effect of arachidonic acid on the microsomal desaturation of linoleic into γ-linolenic acid and their simultaneous incorporation into the phospholipids

Abstract 1. 1. [1-14C]Linoleic acid is desaturated by the microsomes of rat liver to [1-14C]γ-linolenic acid in vitro but the addition of [3H] arachidonic acid increases the conversion. 2. 2. During this reaction [1-14C]linoleic and [1-14C]γ-linolenic acids were mainly incorporated into the choline glycerophosphatides. Smaller amounts were found in ethanolamine glycerophosphatides, neutral lipids, free acids, CoA derivatives and unidentified lipids. 3. 3. [3H] Arachidonic acid was also found in the same lipids and interfered with the incorporation of 14C-labeled acids into phospholipids. The interference was greater for [1-14C]linoleic than for [1-14C]γ-linolenic acid. Therefore, it provoked not only an increase of the [1-14C]linoleic fixed at the application point of the thin-layer chromatogram in silica gel G, where the presence of [1-14C]linoleyl-CoA was recognized, but also increased the [1-14C]γ-linolenic acid synthesis and changed the whole distribution pattern in the lipids. 4. 4. The addition of increasing concentrations of either active or inactivated microsomes eliminated arachidonic acid-activating effect. Neither lecithin nor Tween 20 replaced inactive microsomes but lysolecithin exactly mimicked its effect. Therefore it is considered that arachidonic acid probably activates linoleic acid desaturation by competing with linoleic acid in the parallel reaction that synthesizes phospholipids. More linoleyl-CoA would then be available for the desaturation reaction. Lysolecithin would eliminate the effect esterifying the arachidonic acid.

Effects of estradiol and environmental temperature changes on rat liver Δ6 microsomal desaturase activity

The regulation of Δ6 desaturase activity by environmental temperature changes was studied in the microsomal membranes from female and ovariectomized female rat liver. Female rats adapted at 30–32 C for 20–25 days and then shifted to 13–15 C for 5 days showed an increased Δ6 desaturase system. Ovariectomized rats adapted under the same conditions did not show significant changes in this enzyme. The fatty acid compositions of microsomal phosphatidylcholine showed a decrease in arachidonic acid in female rats at 30 C compared to females at 15 C and ovariectomized rats at both temperatures. These results suggest that a modification of ovaric sex hormone levels might be responsible for the different Δ6 desaturase activity in female rats acclimated at both temperatures. In this regard, serum estradiol radioimmunoassay yielded slight differences between the two groups of female rats, suggesting that estradiol could play a role in the regulation of the Δ6 desaturase. The administration of a pharmacological dose of 17-β estradiol to female and ovariectomized rats kept at 30 and 15 C decreased the Δ6 microsomal desaturase activity. These data suggest that estradiol levels are involved in the regulation of the Δ6 desaturase during cold adaptation.

Effect of dietary glycerol on the [1−14C]stearic acid and [1−14C]linoleic acid desaturation of normal and diabetic rats

Abstract 1. 1. The in vivo Δ 9 -desaturase activity was measured in normal and diabetic rats by the intraportal injection of [1- 14 C]stearic acid. 2. 2. Labeled oleic acid was found mainly in 1,2-diglycerides and triglycerides, while most of the [1- 14 C]stearic acid was recovered in the phospholipid fraction in all the groups of rats. 3. 3. Dietary glycerol was able to partially restore the Δ 9 -desaturase activity depressed by the diabetic state. 4. 4. The in vitro Δ 9 -desaturation of stearic acid and Δ 6 -desaturation of linoleic acid were depressed in the diabetic rats. 5. 5. Dietary glycerol depressed the activity of the Δ 6 -desaturase but had no effect on the Δ 9 -desaturase activity in normal rats. 6. 6. The Δ 9 -desaturase activity was partially recovered by dietary glycerol in the diabetic rats, while no effect was observed in the activity of Δ 6 -desaturase. 7. 7. The increase in the saturated fatty acid synthesis by dietary glycerol in the diabetic rat may promote an increase in the Δ 9 -desaturase activity by adaptive enzyme formation. 8. 8. The depression of Δ 6 -desaturase activity in the normal rats by the high glycerol diet may be related to glycerol metabolism, probably at the α-glycerophosphate step.

Effect of environmental temperature changes on rat liver fatty acid desaturases

Female rats warm-adapted at 30–32 C for 20–25 days and then shifted to 13–15 C for 12, 24, 48, 72 and 120 hr showed that Δ9 desaturase and fatty acid synthetase activity decay after 24 hr of cold exposure, while Δ6 and Δ5 desaturases were increased after this period of time. These results were confirmed by an increase of arachidonic acid of heart and liver microsomes phosphatidylcholine and a decrease of oleic acid. Neither NADH-cyt b5 reductase nor NADH-cyt c reductase activity of liver microsomes were significantly affected. Male rats warm-adapted under the same conditions and then shifted to 13–15 C for 120 hr did not show significant changes in fatty acid synthetase, Δ9 and Δ6 desaturases and enzymes of the microsomal electron transport chain. Therefore, the desaturase response to environmental temperature changes could be plausibly linked to female hormones.

Effect of cold environment on hepatic microsomal Δ6 and Δ9 desaturase activity of male rats

Male rats maintained at 24 C and then shifted to 5 C for 5 days increased food intake and decreased in growth rate and food conversion. No modification was observed in Δ6 desaturase activity, while Δ9 desaturase activity decreased after this period of time. These results were confirmed by liver microsomal and mitochondrial fatty acid composition. The phospholipid composition of liver microsomes was unaltered, whereas in mitochondria, phosphatidylcholine and sphingomyelin decreased and phosphatidylethanolamine increased due to the cold environment. The influence of food intake and weight changes on fatty acid metabolism was studied using (i) rats maintained at 5 C with restricted food intake to match the food intake of those kept at 24 C with food ad libitum and (ii) rats maintained at 24 C whose food intake was also restricted so that their growth rate would be the same as that of rats maintained at 5 C with food ad libitum, respectively. These results indicate that the negative metabolic balance state of these cold conditions is not an active factor modifier of Δ6 desaturase activity, whereas it decreases Δ9 desaturase activity, reflecting the lipogenic characteristics of the latter enzyme.

Lipid digestion, absorption and transport in Triatoma infestans

Abstract 1. 1. 1-14C Oleic acid and glyceryl-tri-1-14C oleate were fed to Triatoma infestans and their digestion, absorption and incorporation in hemolymph lipids, were investigated. 2. 2. Four hours after feeding labeled oleic acid, significant radioactivity was only found in midgut and hemolymph lipids. Little labeling was observed in the fat body at this time and significant radioactivity was only recovered after 8 hr. 3. 3. Four hours after feeding, 14C oleic acid was largely incorporated to the diacylglycerols of the hemolymph high density lipoprotein (HDL) ( d ⋍ 1.11–1.15 g/ml ) indicating that this lipoprotein is the principal carrier of absorbed fatty acids. 4. 4. Glyceryl-tri-1-14C oleate was hydrolyzed in midgut and the resulting fatty acids were absorbed and transported by the hemolymph as diacylglycerol molecules.

Effect of different amino acid diets on δ5, δ6 and δ9 desaturases

A high-protein diet with 45% calories from casein increased δ6 desaturase activity in rat-liver microsomes. High-protein diets with 45% calories from a synthetic mixture of amino acids in the same proportion as casein decreased the δ9 desaturase, slightly increased the δ5 desaturase and greatly increased δ6 desaturase activities compared with a high-carbohydrate diet. The elimination of phenylalanine and tyrosine from the synthetic mixtures of amino acids increased the δ6 desaturase activity. Massive amounts of phenylalanine or tyrosine in the diet inhibited δ6 desaturase activity. Tyrosine and phenylalanine may, by conversion to tyrosine, decrease the activity of the δ6 desaturase.