Desaturation Of Stearic Acid Research Articles

Circadian rhythm of fatty acid desaturation in mouse liver.

AbstractA study was made of the diurnal changes in liver microsomal desaturation of labeled stearic, linoleic and α‐linolenic acids to oleic, γ‐linolenic and octadeca‐6,9,12,15‐tetraenoic acids, respectively. C3H‐S mice were used and were exposed to light‐dark cycles. A circadian rhythm was observed for stearic acid desaturation, and a different one for linoleic acid. Linoleic and α‐linolenic desaturation had similar responses in the day cycle. This would indicate that different mechanisms control the oxidative desaturations of the fatty acids in the 9 and 6 carbons. The fatty acid composition of the whole liver and liver microsomes also showed variations. Remarkable oscillations were observed for stearic and oleic acids. Neither the total protein synthesis nor the free fatty acid concentration in the microsomes followed a rhythm parallel to the desaturation of the studied fatty acids. The injection of cycloheximide 4 hr before measuring the desaturation modified the circadian variation of both the 9 and 6 desaturations. The modification induced by cycloheximide was considered to indicate that both variations are related to the synthesis of specific proteins but not to that of a degradative or inhibitory protein.

The effect of methyl sterculate on oleic acid synthesis in the hen

AbstractThe enzymic desaturation of saturated fatty acids to monoenes in animals and plants is inhibited by cyclopropene fatty acids, such as sterculic acid. Labeled acetic and stearic acids were administered to laying hens which had received methyl sterculate in the diet for long periods, and the incorporation of the label in the eggs and liver was studied. The egg was used as a “biological trap” to study the metabolism of the hen in relation to its diet. Maximum incorporation of label was observed in the third or fourth egg laid after administration of the labeled compound. Dietary methyl sterculate reduced the incorporation of stearic acid into egg yolk lipids, but the incorporation of acetate was not affected. The formation of oleic acid was inhibited by methyl sterculate irrespective of whether the prescursor was acetate or stearate acid. In laying hens receiving methyl sterculate for long periods, no evidence could be obtained for the biosynthesis of oleic acid by an alternative pathway which did not involve the desaturation of stearic acid. The validity of comparing the ratio of the specific activities of stearic acid and oleic acid in control birds with the corresponding ratio obtained for birds receiving methyl sterculate is questioned, because the sizes of the metabolic pools of the product and precursors may be quite different for the two groups of birds.

Ring position in cyclopropene fatty acids and stearic acid desaturation in hen liver.

AbstractFour cyclopropene fatty acids, having the double bond of the cyclopropene ring at the 8,9, 9,10, 10,11 and 11,12 positions, respectively, were tested as inhibitors of stearic acid desaturation by the desaturase enzyme system of hen liver. The first three were powerful inhibitors, but the last was not. The cyclopropene acids with the 9,10 and 10,11 double bonds were equally strong inhibitors, while the acid with the 8,9 double bond was less effective. To account for the specificity of those cyclopropene fatty acids in which the C9 or C10 carbon atom is included in the cyclopropene ring, it is suggested that the conformation and structure of the CoA derivatives of these acids is such that they can irreversibly occupy the site on the enzyme responsible for 9,10‐desaturation.

Synthesis of unsaturated fatty acids in chick embryo liver.

Oxidation, synthesis, and desaturation of fatty acids were assessed in chick embryos and embryonic liver. No differences in the oxidation of palmitate-1-14C and oleate-1-14C by intact embryos and embryo-liver homogenates were found. De novo fatty acid synthesis and microsomal elongation of fatty acids were detected in embryo-liver homogenates, but the activities were low as compared with chick liver. The specific activities of the mitochondrial system of fatty acid elongation were similar in embryo and chick liver. Stimulation of the desaturation of stearic acid was achieved by the substitution of glucose for fatty acids in the culture medium and abolished by the addition of cyclopropene fatty acids to the medium. The hypothesis is advanced that in chick embryos, the rate of desaturation of fatty acids synthesized de novo is less than that of postembryonic liver, and that as a consequence, the liver of embryos cannot maintain the proportion of unsaturated to saturated fatty acids found in yolk.

Inhibition of desaturation of stearic acid in livers of rats fed ethionine.

AbstractThe effect of ethionine on the conversion of stearic acid to oleic acid was studied. Rats were fed essential fatty acid (EFA) deficient diet for three weeks, after which time half the animals were fed 0.25% DL‐ethionine for nine additional days. Seventeen hours prior to killing, they were fed a slurry of the diet containing 18‐14C‐stearic acid. Liver triglycerides and phospholipids were extracted and separated and their fatty acid composition and the distribution of radioactivity between stearic and oleic acid was determined. In the tissues studied, oleic acid was maintained at control levels in ethionine‐fed rats, but eicosatrienoic acid was significantly depressed. Distribution of radioactivity and specific activity of oleic acid in the triglycerides and phospholipids were significantly reduced by the analogue. In vitro studies of desaturation and chain elongation reactions, with liver microsomes, using 18‐14C‐stearic and 1‐14C‐linoleic acids as substrates, showed that ethionine depressed the synthesis of oleic acid from stearic and γ‐linolenic from linoleic acid. Elongation of linoleic adie to a 20∶2 fatty acid was unaffected by ethionine. Therefore, the results showed that ethionine inhibited desaturation of stearic to oleic acid in vivo and in vitro and probably also impaired the desaturation of oleic to octadeca‐6, 9‐dienoic acid. Maintenance of control levels of oleic acid in the tissues of ethionine‐fed, EFA deficient rats suggested the presence of synthetic pathways for oleic acid other than via desaturation of stearic acid.

Effect of oleic and linoleic acids on the monodesaturation in vitro of stearic acid by the livers of patients suffering from malignant neoplastic diseases.

The desaturation of stearic acid to oleic acid was examined in vitro using 10, 000×g supernatant fraction of the liver specimens biopsied from the patients. The desaturation rates by the liver specimens from the malignant neoplastic cases were relatively lower than those in the nonmalignant cases. The addition of oleic and linoleic acids into the reaction mixture inhibited the desaturation of stearic acid-1-14C by the liver specimens from the non-malignant cases, whereas in the liver specimens from the malignant neoplastic cases such inhibitory effects appeared to be lost.

Alternate route for the biosynthesis of oleic acid in the rat

1. 1. Adult rats were given by stomach tube 10 μC of methyl [1- 14]stearate dissolved in either corn oil or Sterculia foetida seed oil. After 3 h they were injected with 200 μC of [ 3H]acetate and were sacrificed 1 h later. The 3H and 14C specific radioactivities of the stearic acid in the liver lipids of the corn oil controls were nine times as high as in the oleic acid. When S. foetida oil was in the diet, the 14C ratio was about 1500 whereas the 3H ratio was only 14, showing that stearic acid desaturation to oleic acid was inhibited but not acetate conversion to oleic acid. 2. 2. When a similar study was carried out in which methyl [1- 14C]laurate and methyl [11,12- 3H 2]stearate were given, the 3H ratio in the corn oil controls was about 8 and the 14C ratio was about 2, indicating that laurate acted as a precursor for oleic acid biosynthesis. Inclusion of S. foetida seed oil resulted in an increase in the 3H ratio to about 1600 whereas the 14C ratio was increased to only 12, showing that lauric like acetate conversion is not inhibited by cyclopropene fatty acids. Permanganate oxidation studies of the isolated octadecenoic acids indicated that when S. foetida seed oil was given, about 90% of the octadecenoate radioactivity was in oleic, and 90% of the oleic acid activity due to 14C was in the azelaic acid fraction. This suggests the intact utilization of lauric acid for oleic acid synthesis, probably by β,γ-desaturation followed by elongation.

Inhibition by cyclopropene fatty acids of the desaturation of stearic acid in hen liver

The mechanism of the hardening of body fats of animals by dietary lipids which contain cyclopropene fatty acids has been studied. Dietary methyl sterculate increased the stearic acid content of egg yolk lipid and decreased the activity of the stearic acid desaturase system of hen liver. The cyclopropene fatty acids were specific inhibitors of the stearic acid desaturase system of hen livers since other fatty acids, including two possible metabolites of sterculic acid, failed to inhibit the system at equivalent concentrations. Sterculic acid was a more effective inhibitor of the system than malvalic acid. Kinetic studies have shown that the inhibition is irreversible. Apparent kinetic constants were determined for the system.The results support the hypotheses that cyclopropene fatty acids inactivate an essential component of the desaturase system, probably by combination with-SH groups, and that this inhibition causes many of the effects of dietary cyclopropene fatty acids, including permeability disorders of eggs.

The effect of insulin on monounsaturated fatty acid synthesis in diabetic rats. The stability of the informational RNA and of the enzyme system concerned with fatty acid desaturation

The effect of single injections of insulin on insulin-induced monounsaturated fatty acid synthesis in the epididymal adipose tissue of diabetic rats, was determined. Olefin synthesis increased slowly to a maximum between 48 and 72 h, remained high for 24 to 48 h and then declined rapidly to the low levels characteristic of diabetes. The level of enzyme activity attained and the duration of the effect were dependent upon the dose of insulin administered. To determine whether the informational RNAribosome complex formed under the influence of insulin was more stable than the enzyme induced, young normal rats were given either actinomycin D or puromycin, inhibitors of RNA and protein synthesis, respectively, and the olefin synthesis measured in vitro at intervals of time during continuous depression of RNA or protein synthesis. In animals receiving actinomycin D, 15 μg per 100 g, at 12-h intervals, desaturating enzyme activity was reduced to one-half the initial value in 19 h; the comparable time for animals receiving puromycin, 2.5–5.0 mg per 100 g every 2 to 3 h, was 3.5 h. It was concluded that the informational RNA-ribosomal complex directing the synthesis of the enzyme (s) concerned with stearic acid desaturation is significantly more stable than the enzyme formed.

The effects of thyroxine on the pattern of fatty acid synthesis in rat liver

1. (1) The effects of thyroxine on the pattern of fatty acid synthesis from [1− 14C]-acetate by rat-liver slices have been investigated. Treatment with this hormone, both at physiological and at pharmacological doses, stimulates the incorporation of [1− 14C]acetate into stearic acid, into the octadecenoic acids and into the poly-unsaturated fatty acids. 2. (2) The increased incorporation of acetate into the octadecenoic acid fraction appears to be associated with an increased desaturation of stearic acid both in liver slices and in microsomal systems, and also with an enhanced activity of stearoyl-CoA desaturase. 3. (3) Degradation studies on the stearic acid synthesised in slices from control and from thyroxine-treated animals suggest that the increased formation of stearic acid may be by synthesis de novo. It appears that there may be an alteration in the rate of stearic acid synthesis in combined supernatant and microsomal systems when microsomes from thyroxine-treated animals are substituted for microsomes from normal animals.

Immediate fate of albumin-bound [1- 14C]stearic acid following its intraportal injection into carbohydrate refed rats : Early course of desaturation and esterification in the liver

1. 1. [1- 14C]Stearic acid in rat serum or human serum albumin solution was injected intraportally into carbohydrate refed, immature male rats weighing 80–100 g. Livers were removed at 5, 10, 20, 30 and 60 sec after injection. 2. 2. During this time there is rapid incorporation of label into liver 1,2-diglycerides, triglycerides and phospholipids. 3. 3. 1,2-Diglycerides are present in a concentration of about 1 μmole per whole liver in these small rats. The insignificant amounts of label found in fractions expected to contain phosphatidic acids and the absence of a lag in the incorporation of stearic acid into 1,2-diglycerides suggest that phosphatidic acids must be present in exceedingly low concentrations. 4. 4. In two experiments one third to one half of the label in liver total esters was recovered in oleic acid at 60 sec. 5. 5. At all times oleic acid label was found mainly in triglycerides and 1,2-diglycerides, while most of the stearic acid label was recovered in the phospholipid fraction. 6. 6. Further fractionation of total 1,2-diglycerides and total glycerophosphatides according to degree of unsaturation was achieved by conversion to acetylated 1,2-diglycerides and subsequent thin-layer chromatography on silver nitrate-silica gel. 7. 7. The predominant glycerophosphatide subgroup contains arachidonic acid balanced mainly by stearic and some palmitic acid. A poorly defined fraction contains an acid tentatively identified as docosahexaenoic acid, balanced mainly by palmitic and some stearic acid. The equivalent subfractions are also identified in the 1,2-diglycerides ; however, the largest fraction in the latter is the mono-unsaturated one, containing palmitic and oleic acid, but almost no stearic acid. 8. 8. The distribution at different times of oleic and stearic acid label between the ester fractions and subfractions found in these experiments permits the following conclusions : (a) Results are entirely consistent with the assumption that desaturation of stearic acid in the intact rat liver occurs exclusively at the stearoyl-CoA level, pro- ducing oleoyl-CoA. (b) Incorporation of stearic acid into glycerophosphatides by direct acylation as proposed by Lands, accounts for nearly all the stearic acid label introduced into that fraction. Total synthesis de novo, at least of the polyenoic fatty acid-containing glycerophosphatides, proceeds at a much slower rate, (c) In these refed rats an approximately equal amount of oleic acid label is introduced into triglycerides via preliminary formation of 1,2-diglycerides and with the third fatty acid unit used to acylate those 1,2-diglycerides.