Tissue culture of cocoa bean (Theobroma cacao L.): Incorporation of fatty acids into lipids of cultured cells

Suspension cell cultures of cocoa bean rapidly incorporated palmitic, stearic, oleic and linoleic acids into cellular lipids. Thus, 75 and 20% of [1-¹⁴C] palmitic acid was incorporated into polar lipids and triglycerides, respectively, after 48 hr. When [1-¹⁴C] oleic and [1-¹⁴C] linoleic acid were added separately, polar lipids consistently contained most of the radioactive fatty acids. Ca. 60% of the stearic acid accumulated as unesterified fatty acid in the cells. Palmitic and stearic acid were not desaturated, but oleic acid and linoleic acid were further desaturated. The kinetics of conversion of oleic acid and linoleic acid suggested a sequential desaturation pathway of 18∶1→18∶2→18∶3 in cocoa bean cell suspensions.     

Plasma clerance and hepatic utilization of stearic,myristic and linoleic acids introducedvia chylomicrons in rats

The primary objective of the present study was to compare the rates of plasma clearance and hepatic utilization of stearic (18∶0), myristic (14∶0) and linoleic (18∶2) acids, as introducedvia chylomicrons. Lymph chylomicrons were specifically labeledin vivo with [¹⁴C]stearic and (SA), [¹⁴C]myristic acid (MA), or [¹⁴C]linoleic acid (LA) by infusing donor rats intraduodenally with the labeled fatty acids in a lipid emulsion. Following intravenous injection of recipient rats with the labeled chylomicrons, the rates of plasma clearance and incorporation of the label in triglycerides (TG), phospholipids (PL) and other lipids in the liver were compared at 5, 15 and 30 min. [¹⁴C]SA was cleared at a slightly faster rate (t_1/2=7.0 min) than [¹⁴C]MA (t_1/2=8.1 min) and [¹⁴C]LA (t_1/2=8.0 min) (P<0.05). [¹⁴C]SA was accumulated in the liver at a significantly faster rate than [¹⁴C]MA and [¹⁴C]LA. At the peak (15 min) of hepatic uptake, 30.3% of [¹⁴C]SA, 26.2% of [¹⁴C]LA and 21.9% of [¹⁴C]MA were recovered in the liver. At 30 min, 33.5% of [¹⁴C]SA was taken up by the liver, whereas 27.8% of [¹⁴C]LA and only 15.2% of [¹⁴C]MA were removed. In the liver, the percentage of [¹⁴C]SA incorporated into PL steadily increased with time, whereas the percent-age incorporated into TG decreased. [¹⁴C]SA was preferentially incorporated into PL at all time intervals, as compared with [¹⁴C]MA and [¹⁴C]LA. At 30 min, 38.6% of [¹⁴C]SA was found in PL, and only 5.2% of [¹⁴C]MA and 12.0% of [¹⁴C]LA were present in PL. A large proportion of hepatic [¹⁴C]MA remained unesterified (free fatty acid) throughout the 30-min period, with a small proportion incorporated into PL and TG. Of the total liver¹⁴C radioactivity recovered at 30 min, 63.8% of [¹⁴C]MA, 48.8% of [¹⁴C]LA and 25.5% of [¹⁴C]SA were found unesterified. During 30 min, a significantly greater amount of [¹⁴C]MA (76.9%) was oxidized in both the liver and the peripheral tissue combined, compared with [¹⁴C]LA (64.7%) and [¹⁴C]SA (61.2%). A higher proportion of [¹⁴C]LA was incorporated into TG than into PL at all time intervals. No differences were noted in the relative distribution of¹⁴C in cholesterol and other lipids among the three fatty acids. Using labeled fatty acids incorporatedin vivo into chylomicrons, the present study demonstrated that SA, MA and LA are distinctly different in their metabolic behavior. During the initial 30 min after their entry into the blood, 92–95% of the fatty acids were cleared. During this early phase of metabolism, [¹⁴C]SA was preferentially utilized for liver PL synthesis, whereas [¹⁴C]LA was better incorporated into TG. [¹⁴C]MA was poorly incorporated into hepatic lipids, but was preferentially oxidized in the liver or utilized by the peripheral tissue.     

Fatty acid synthesis in the oil palm (Elaeis guineensis): Incorporation of acetate by tissue slices of the developing fruit

Oil palm (E. guineensis) fruits at three stages of development were studied. At week 12–13 after anthesis, the endosperm had started accumulating oil and tissue slices incorporated [1-¹⁴C] acetate into fatty acids which resembled those found in the mature endosperm. The mesocarp contained very little oil and incorporated acetate into polar lipids. At week 16–17, the mesocarp started to accumulate oil; this was reflected in the [¹⁴C] lipid products from acetate incubation. At or just prior to this stage, an increase in the endogenous linoleic and linolenic acid content and the increase in fruit size indicated cellular growth in the mesocarp tissue. At week 20–21 the fruit was ripe, and both endosperm and mesocarp tissues were filled with storage oil. [¹⁴C] Fatty acids synthesized from acetate by mesocarp slices at this stage were the same as the endogenous storage fatty acids in bothE. guineensis andE. oleifera. A very weak fatty acid synthesizing activity was seen in the mature endosperm, but the products had no relationship to the storage lipid.     

Elongation of (n−9) and (n−7)cis-monounsaturated and saturated fatty acids in seeds ofsinapis alba

Lipids in developing seeds ofSinapis alba contain appreciable proportions of (n−7)octadecenoic (vaccenic) acid besides its (n−9) isomer (oleic acid), whereas the constituent very long chain (>C₁₈) monounsaturated fatty acids of these lipids are overwhelmingly composed of the (n−9) isomers. Cotyledons of developingSinapis alba seed use [1-¹⁴C]acetate, [1-¹⁴C]malonate or [1,3-¹⁴C]malonyl-CoA for de novo synthesis of palmitic, stearic and oleic acids and for elongation of preformed oleic, vaccenic and stearic acids to their higher (n−9), (n−7) and saturated homologs, respectively. Moreover, elongation of preformed (n−7)palmitoleic acid to vaccenic acid is observed. Stepwise C₂-additions to preformed oleoyl-CoA by acetyl-CoA or malonyl-CoA yielding (n−9)icosenoyl-CoA, (n−9)docosenoyl-CoA and (n−9)tetracosenoyl-CoA are by far the most predominant reactions catalyzed by the elongase system, which seems to have a preference for oleoyl-CoA over vaccenoyl-CoA as the primer. The pattern of¹⁴C-labeling of the very long chain fatty acids formed from either acetate or malonate shows a close analogy in the mode of elongation of monounsaturated and saturated fatty acids.     

Saturated fatty acids >C20 are not activated by acid:CoA ligase in rat brain or liver?

The formation of long-chain saturated acyl-[³H]CoA and [1-¹⁴C] acyl-[³H]CoA by rat brain microsomes and rat liver was examined. Acyl-CoA formation was markedly decreased as fatty-acid chain length increased from C₁₆ to C₂₀. No biosynthesis of behenyl-[³H] CoA or [1-¹⁴C] lignoceryl-[³H] CoA was observed. The results suggest that long-chain saturated fatty acids >20 carbons in length are not activated by acid:CoA ligase to form acyl-CoA.     

Hepatic metabolism of 1-14C octanoic and 1-14C margaric acids

The hepatic metabolism of 1-¹⁴C margaric acid, a 17 carbon long chain saturated fatty acid which is present in the liver in trace amounts, was compared with 1-¹⁴C octanoic acid and 1-¹⁴C palmitic acid to determine if the enhanced oxidation of medium chain fatty acids to CO₂ was dependent on fatty acid chain length or the endogenous pool size of the fatty acid substrate. Despite the fact that endogenous margarate is present in trace amounts, there was no significant difference in the oxidation of margarate and palmitate to CO₂, while the oxidation of octanoate to CO₂ was significantly more rapid. Both margarate and palmitate were more readily incorporated into lipid soluble products in contrast to the low rate of incorporation of octanoate. However, margarate was less readily incorporated into triglyceride, phospholipid and monoglyceride than palmitate. These studies suggest that the chain length rather than hepatic content of the fatty acid determines whether the carboxyl group of equimolar amounts of a 1-¹⁴C-carboxyl labeled fatty acid will be preferentially oxidized to CO₂ or incorporated into tissue lipid in the liver.     

Pulmonary surfactant lipid synthesis from ketone bodies,lactate and glucose in newborn rats

The contribution of acetoacetate (AcAc), β-hydroxybutyrate (βOHB), lactate and glucose to pulmonary surfactant lipid synthesis in three-to five-day-old rats was measured. Minced lung tissue was incubated with³H₂O and [3-¹⁴C]AcAc, [3-¹⁴C]βOHB, [U-¹⁴C]lactate or [U-¹⁴C]glucose, and the radioactivity incorporated into surfactant lipids was measured. When expressed as nmol of substrate incorporated/g lung tissue per four hr, lactate was incorporated more rapidly than other substrates into total surfactant lipids and phosphatidylcholine (PC). There was no difference in the rates of incorporation of lactate, AcAc or glucose into disaturated PC (DSPC). Substrates other than glucose were incorporated almost exclusively into fatty acids, whereas 60–80% of glucose incorporated into surfactant phospholipids was found in fatty acids, with the remaining in glyceride-glycerol. When expressed as nmol acetyl units incorporated/g lung tissue per four hr, the rates of AcAc, lactate and glucose incorporation into total surfactant fatty acids were comparable. Glucose incorporation into DSPC and PC was greater than that of AcAc and lactate. When glucose was the only exogenous substrate added to the incubation medium, it contributed 37% of total surfactant fatty acids synthesized de novo. In the presence of other substrates, the contribution of glucose to de novo fatty acid synthesis dropped to 14–20%. In the presence of unlabeled glucose,¹⁴C-labeled AcAc, lactate and βOHB contributed 52%, 40% and 19%, respectively, of the total fatty acids synthesized de novo. The rate of βOHB incorporation into surfactant lipids was only about 50% that of other substrates and was accompanied by low activity of β-hydroxybutyrate dehydrogenase measured for newborn lung. These results demonstrate that AcAc and lactate are important precursors for surfactant lipids in neonatal rat lung.     

Tissue culture of cocoa beans (Theobroma cacao L.): Incorporation of acetate and laurate into lipids of cultured cells

Suspension cultures of cocoa bean tissue readily incorporated exogenous acetate into lipids. The distribution of radioactivity from acetate in individual lipid classes after 48 hr was 20, 5, 1, 15, 25, and 35% in triglycerides, diglycerides, free fatty acids, sterol esters, sterols and polar lipids, respectively. The labeled acetate was rapidly incorporated into various fatty acids within 2 hr. The [1-¹⁴C] saturated fatty acids declined slightly after 4 hr, whereas [1-¹⁴C] oleate declined significantly after 2 hr. There was a concomitant increase in [1-¹⁴C] linoleate. The radioactivity associated with linolenate was relatively high up to 4 hr, declined by 24 hr, and then increased again. The kinetics of fatty acid labeling suggested that biosynthesis of linolenic acid in cocoa bean suspension culture may occur via the desaturation of linoleic acid and the chain elongation of dodecatrienoic acid. The patterns of fatty acid radiolabeling following incubation of cells with [1-¹⁴C] laurate was consistent with this mechanism.     

Fatty acid and sterol synthesis by rat small intestine in vitro

Slices of rat jejunum were incubated with [2-¹⁴C]pyruvate, [1-¹⁴C]acetate, or [³H]H₂O to determine lipogenic activity. Under all conditions studied, pyruvate acted as a better precursor than acetate for fatty acid synthesis but not for the synthesis of sterol. Exogenous glucose significantly (P≤0.05) increased the conversion of both pyruvate and acetate to fatty acids. By contrast, fasting resulted in a decrease (p≤0.05) in lipogenic activity. The highest levels of lipogenesis were observed when [³H]H₂O + glucose at a concentration of 20 mM was used. From such experiments, the absolute rate of fatty acid synthesis in the tissue preparation was calculated: 734±54 nmoles acetyl units incorporated into fatty acids/g tissue/hr.     

The structure of polyenoic odd- and even-numbered fatty acids of mullet (Mugil cephalus)

Mullet oil contains more than 25% straight-chain odd-numbered fatty acids. Odd- and even-numbered components of chain lengths C₁₅ to C₂₀ were isolated and their structures determined. The vinylmethane rhythm prevails in all polyun-saturated acids. Numerous homologs have their double bonds in identical positions, relative to the carboxyl group, as for example, 舥^9,12- and 舥^6,9,12-C₁₅, -C₁₆, -C₁₇ and -C₁₈ acids. The terminal structures which are characteristic for oleic, linoleic, etc., families are not found in the unsaturated odd-numbered acids. The results show: that the proximal structure has greater influence than the terminal structure on the biosynthesis of unsaturated odd-numbered acids; that chain lengths of 17 and 18 carbon atoms with double bonds in position 9 are crucial for synthesis of the polyenoic C₁₉ and C₂₀ acids; that chain lengths C₁₅ and C₁₆ with double bonds in position 9 are suitable for desaturation but that they are not suitable for desaturation after elongation. These specifications bring all acids of mullet into a rational order and reflect their possible interconversions. Presently, such classification has only limited predictive value in regard to the physiological properties of polyunsaturated acids. However, the new definitions for grouping the polyunsaturated fatty acids lead to interesting working hypotheses.     

Lipogenesis in the developing brain from intracranially administered [1-14C] acetate and [U-14C] glucose

Fifteen-day-old rats divided into two groups were given [1-¹⁴C]acetate or [U-¹⁴C] glucose by intracranial injection and were sacrificed after 1 hr. Analysis of lipids from the two groups showed differences in the incorporation of radioactivity in the polar lipids and cholesterol. Analysis of brain fatty acid showed that whereas radioactivity from acetate was incorporated into saturated, monoand polyunsaturated fatty acids, the radioactivity from [U-¹⁴C] glucose was found only in 16∶0, 18∶0, and 18∶1. No radioactivity was found in polyunsaturated fatty acids even after concentration of this fraction by AgNO₃:SiO₂ thin layer chromatographic method. This difference is discussed in hypothetical terms of nonhomogeneous acetyl CoA pool, formation of acetyl CoA from glucose exclusively inside the mitochondria, and activation of injected acetate to acetyl CoA.     

Fatty acid metabolism in marine fish: Low activity of fatty acyl Δ5 desaturation in gilthead sea bream (Sparus aurata) cells

Marine fish have an absolute dietary requirement for C₂₀ and C₂₂ highly unsaturated fatty acids. Previous studies using cultured cell lines indicated that underlying this requirement in marine fish was either a deficiency in fatty acyl Δ5 desaturase or C_18–20 elongase activity. Recent research in turbot cells found low C_18–20 elongase but high Δ5 desaturase activity. In the present study, the fatty acid desaturase/elongase pathway was investigated in a cell line (SAF-1) from another carnivorous marine fish, sea bream. The metabolic conversions of a range of radiolabeled polyunsaturated fatty acids that comprised the direct substrates for Δ6 desaturase ([1-¹⁴C]18∶2n−6 and [1-¹⁴C]18∶3n−3), C_18–20 elongase ([U-¹⁴C]18∶4n−3), Δ5 desaturase ([1-¹⁴C]20∶3n−6 and [1-¹⁴C]20∶5n−3), and C_20–22 elongase ([1-¹⁴C]20∶4n−6 and [1-¹⁴C]20∶5n−3) were utilized. The results showed that fatty acyl Δ6 desaturase in SAF-1 cells was highly active and that C_18–20 elongase and C_20–22 elongase activities were substantial. A deficiency in the desaturation/elongation pathway was clearly identified at the level of the fatty acyl Δ5 desaturase, which was very low, particularly with 20∶4n−3 as substrate. In comparison, the apparent activities of Δ6 desaturase, C_18–20 elongase, and C_20–22 elongase were approximately 94-, 27-, and 16-fold greater than that for Δ5 desaturase toward their respective n−3 polyunsaturated fatty acid substrates. The evidence obtained in the SAF-1 cell line is consistent with the dietary requirement for C₂₀ and C₂₂ highly unsaturated fatty acids in the marine fish the sea bream, being primarily due to a deficiency in fatty acid Δ5 desaturase activity.     

Asymmetric distribution of decanoate in triacylglycerol synthesized in vitro by mammary glands of lactating mice

Slices, prepared from the mammary glands of lactating mice, were incubated with either [1-¹⁴C]acetate, [U-¹⁴C]glucose, or [1-¹⁴C]decanoate. From all 3 substrates, radioactivity in the synthesized lipids was found mainly in triacylglycerols (TG). When acetate or glucose served as substrate, decanoate (C₁₀) accounted for 24% of the fatty acids in TG. Hydrolysis of the TG by pancreatic lipase yielded [¹⁴C] fatty acids which had relatively more C₁₀ (38%) than did either of the other hydrolysis products mono- or diacylglycerol (14–17%). However, when TG produced by slices from C₁₀ were hydrolyzed, the acid was found to be esterified equally at the C-1, C-2 and C-3 of glycerol. Thus, when fatty acids are synthesized de novo and are converted to TG by gland slices, C₁₀ is predominantly located in the C-3 position, a finding in accord with the situation in milk TG, although such preferential incorporation does not occur when the free acid is presented to the tissue slices.     

Biosynthesis of unsaturated fatty acids in the diatomPhaeodactylum tricornutum

The biosynthesis of fatty acids in the diatomPhaeodactylum tricornutum was studied. The diatom was incubated with sodium [1¹⁴C] acetate and the acids [1-¹⁴C] palmitic, [1-¹⁴C] stearic, [1-¹⁴C] linoleic and [1-¹⁴C] α-linolenic. The distribution of radioactivity in the products was determined by gas liquid radiochromatography. The diatom synthesized “de novo” not only saturated and monounsaturated fatty acids, but also linoleic, α-linolenic and other fatty acids including the highly polyunsaturated 20∶5ω3 and 22∶6ω3. When labeled acetate, stearic, α-linolenic or even linoleic acid were incubated with the diatom, the polyunsaturated C₂₀ fatty acids synthesized belonged predominantly to the ω 3 family. The existence of Δ9, Δ6, Δ5, Δ4, ω6 and possibly ω3 desaturases inP. tricornutum is suggested. Member of the Carrera del Investigador Científico of the Comisión de Investigaciones Científicas de la Provincia de Buenos Aires. Member of the Carrera del Investigador Cientifico of the Consejo Nacional de Investigaciones Cientificas y Técnicas.     

Fatty acid specificity of glyceride synthesis by homogenates of bovine mammary tissue

Fatty acid esterification by cell free preparations of bovine mammary tissue was investigated to determine if the type of long chain fatty acid supplied might influence the rate of triglyceride synthesis by that tissue. Homogenates of lactating bovine mammary tissue esterified¹⁴C-fatty acids into glycerides at rates dependent upon chain length and degree of unsaturation. Palmitic, stearic, oleic and linoleic acids were esterified at rates consistent with their concentration in milk fat. A comparison of free fatty acid concentrations of mammary tissue with levels saturating esterification suggested that supply of fatty acids does not limit glyceride synthesis. Certain combinations of fatty acids were facilitory, competitive or inhibitory to esterification. Stearic acid complimented esterification of palmitic and oleic acids. Unlabeledtrans-11-octadecenoic acid did not compete with¹⁴C-palmitate as efficiently in the esterification process as did unlabeledcis-9-octadecenoic acid, indicating that the mammary gland may preferentially esterify thecis-isomer of C-18∶1. Linoleic acid inhibited esterification of palmitic, stearic and oleic acids. Michigan Agricultural Experiment Station Journal Article No. 5100.     

Chain elongation of polyunsaturated fatty acids by vascular endothelial cells: Studies with arachidonate analogues

This study has utilized radiolabeled analogues of arachidonic acid to study the substrate specificity of elongation of long-chain polyunsaturated fatty acids. Human umbilical vein endothelial cells were incubated for 2–72 hr in medium supplemented with 0.9–2.6 μM [¹⁴C]fatty acid, and cellular glycerolipids were analyzed by gas-liquid chromatography with radioactivity detection. Elongation of naturally occurring C₂₀ polyunsaturated fatty acids occurred with eicosapentaenoate (20∶5(n−3))>Mead acid (20∶3(n−9))>arachidonate (20∶4(n−6)). Chain length markedly influenced the extent of elongation of 5,8,11,14-tetraenoates (18∶4>19∶4>20∶4>21∶4); effects of initial double bond position were also observed (6,9,12,15–20∶4>4,7,10,13–20∶4. Neither 5,8,14- nor 5,11,14–20∶3 was elongated to the extent of 5,8,11–20∶3. Differences between polyunsaturated fatty acids were observed both in the initial rates and in the maximal percentages of elongation, suggesting that the content of cellular C₂₀ and C₂₂ fatty acids may represent a balance between chain elongation and retroconversion. Umbilical vein endothelial cells do not exhibit significant desaturation of either 22∶4(n−6) or 22∶5(n−3). By contrast, incubation with 5,8,11,14-[¹⁴C]18∶4(n−4) resulted in formation of both [¹⁴C]20∶5(n−4) and [¹⁴C]22∶5(n−4). The respective time courses for the appearances of [¹⁴C]22∶5(n−4) and [¹⁴C]20∶5(n−5) suggests Δ6 desaturation of [¹⁴C]22∶4(n−4) rather than Δ4 desaturation of [¹⁴C]20∶4(n−4).     

The incorporation of fatty acids of different chain length into liver and biliary lipids in the perfused rat liver

In an attempt to correlate the incorporation of fatty acids (FA) of different chain length into liver and biliary lipids’ isolated rat livers were perfused for 2 h with Krebs-Ringer bicarbonate containing 1% albumin and 10 μmol of [1-¹⁴C]-labeled FA: C₂’ C₈’ C₁₀’ C₁₂’ C₁₆’ and C_18∶1. One to 1.36 μmol of medium-chain fatty acids (MCFA’ C₈’ C₁₀’ and C₁₂) and 6.6 μmol of long-chain FA (LCFA) were incorporated into liver lipids’ 40% of the latter into phosphatidylcholine (PC). ¹⁴C-acetate (13 nmol) was incorporated into biliary cholesterol; ¹⁴C-MCFA contributed only 3.2–5 nmol; LCFA did not lead to newly synthesized cholesterol. Newly synthesized liver PC (2.75 to 3.25%) and newly synthesized liver cholesterol (6.5 to 10%) were secreted into bile. The specific radioactivity of biliary PC after infusion of all-saturated FA was 3.8–6.8 times higher than that of liver PC; for C_18∶1 it was only 1.7-fold. The specific radioactivity of biliary cholesterol’ as compared to liver cholesterol’ was 12 times higher for C₂ and five times higher for MCFA. This indicates that a considerable proportion of the newly synthesized lipids was secreted into bile prior to significant mixing with preexisting liver PC and cholesterol pools. liver PC contained 8% of unchanged ¹⁴C−C₁₂; while ¹⁴C−C₁₀ was not detected. Biliary PC’ in contrast’ contained 18% of unchanged ¹⁴C−C₁₂ and 3% ¹⁴C−C₁₀. These results suggest that after prolonged infusion of medium-chain triacylglycerols/longchain triacylglycerols to patients’ biliary PC may become enriched with MCFA. In addition’ the oxidation of these FA may provide C-2 units which increase cholesterol synthesis.     

Structure-activity relationship of unsaturated fatty acids as mosquito ovipositional repellents

Various straight-chain unsaturated fatty acids from C₁₄ to C₂₄ were evaluated for their ovipositional repellency against gravid females of the southern house mosquitoCulex quinquefasciatus Say, and the relationship between the structures of the fatty acids and their ovipositional repellency was determined. A double bond withZ configuration was prerequisite for an unsaturated fatty acid to be highly repellent;E isomers were less active or even inactive. No relationship was found between the repellency and the number of double bonds in the unsaturated fatty acids. In C₁₈ monounsaturated fatty acids, (Z)-9 acid was more active than (Z)-11 and (Z)-6 acids, indicating that a double bond at the 9 position rendered an acid highly repellent. Among (Z)-9-alkenoic acids of different chain lengths, the most repellent was C₁₈ acid which was also more active than (Z)-11-C₂₀, (Z)-13-C₂₂, and (Z)-15-C₂₄ acids. Oleic[(Z)-9-octadecenoic]acid, which met all these criteria, was the most ovipositionally repellent among the unsaturated fatty acids tested.Diptera: Culicidae.     

Accumulation of neutral lipids by human skin fibroblasts: Differential effects of saturated and unsaturated fatty acids

The accumulation of neutral lipids by human skin fibroblasts grown in medium supplemented with fatty acids has been investigated. GM-10 cells incorporated exogenous fatty acids into both phospholipids and neutral lipids. More [¹⁴C] oleate, linoleate, or linolenate was incorporated into triacylglycerol than was [¹⁴C] palmitate or stearate. Supplementation of medium containing delipidized serum with unsaturated fatty acids resulted in far more stimulation of [¹⁴C] glycerol incorporation into triacylglycerol than did supplementation with saturated fatty acids. Palmitate- and stearate-fed cells incorporated sizable amounts of [¹⁴C] fatty acids and [¹⁴C] glycerol into diacylglycerol as well as triacylglycerol, especially at higher fatty acid concentrations. Increased oleate supplementation from 10–300 μM resulted in increased triacylglycerol synthesis and accumulation of discrete cytoplasmic lipid droplets; palmitate concentrations above 70 μm were toxic. Micrographs of the palmitate-fed cells showed electron translucent slits, suggesting solid depositions of saturated fat, rather than the discrete osmiophilic droplets found in oleate-fed cells. Although GM-10 cells can synthesize fully saturated triacylglycerols, these data suggest that in cells fed saturated fatty acids, solid depositions of neutral lipids may sequester diacylglycerols and thus limit triacylglycerol synthesis.     

Fatty acid desaturase systems of hen liver and their inhibition by cyclopropene fatty acids

Hen liver preparations which desaturate stearic acid at the 9,10 position to form oleic acid have been found to desaturate other saturated fatty acids of carbon chain length from 12 to 20 and 22. The 9,10-monoenoic fatty acid of the same chain length as the substrate fatty acid is the major product formed. Minor amounts of the 10,11- and 11, 12-monoenoic acids are also formed. Maximum desaturation occurred with the C₁₄ fatty acid substrate and with the fatty acids C₁₇ and C₁₈, suggesting the presence of at least two desaturating systems. The cyclopropene fatty acids, sterculic and malvalic acids, inhibited the desaturation of all thefatty acids at the 9,10 position but desaturation at the 10,11 and 11, 12 positions was affected only slightly. The effect is not due to inhibition of the primary activating enzyme, the long chain acyl CoA synthetase. Sterculic acid is a more effective inhibitor than either malvalic acid or sterculyl alcohol, probably because these cyclopropene compounds do not block the desaturating site of the enzyme as completely as sterculic acid.