Synthesis of lipids in isolated nuclei from rat thymus and liver cells

Synthesis of lipids was studied in isolated nuclei from rat thymus and liver cells. On incubation of the isolated nuclei with [2-¹⁴C]acetate and [1-¹⁴C]glycerol, the label was intensively incorporated into phospholipids and with a significantly lower intensity into fatty acids and cholesterol. Only trace amounts of radioactivity were detected in the lipids of chromatin prepared from isolated thymus nuclei after their incubation, and this suggested that lipids were mainly synthesized on the nuclear membrane. On the preincubation of thymus tissue homogenate with [2-¹⁴C]acetate and the subsequent isolation of the nuclei and chromatin, the radioactivity of chromatin lipids was comparable to the radioactivity of nuclear lipids. The findings suggested that in the isolated nuclei the newly synthesized lipids were not transported into chromatin from the nuclear membrane. The specific radioactivities of individual phospholipids and fatty acids were different in the isolated nuclei and in nuclei obtained from preincubated homogenate. Mechanisms of lipid synthesis in isolated nuclei and causes of the different radioactivities of lipids in the isolated nuclei and in the nuclei obtained from the preincubated homogenate are discussed.     

Metabolism of tween-Fatty Acid esters by cultured soybean cells : kinetics of incorporation into lipids, subsequent turnover, and associated changes in endogenous Fatty Acid synthesis

Uptake of Tween-fatty acid esters and incorporation of the fatty acids into lipids by soybean (Glycine max [L.] Merr.) suspension cultures was investigated, together with subsequent turnover of the incorporated fatty acids and associated changes in endogenous fatty acid synthesis. Tween uptake was saturable, and fatty acids were rapidly transferred from Tweens to all acylated lipids. Patterns of incorporation into glycerolipids were similar in cells treated with Tweens carrying [1-¹⁴C]-fatty acids and in cells treated with [1-¹⁴C]acetate, indicating that exogenous fatty acids were used for glycerolipid synthesis essentially as if they had been made by the cell. In Tween-treated cells neutral lipids (which include Tweens) initially accounted for the majority of lipid radioactivity. Radioactivity was then rapidly transferred to glycerolipids. A transient pool of free fatty acids accounting for up to 10% of lipid radioactivity was observed. This was consistent with the hypothesis that fatty acids are transferred from Tweens to lipids by deacylation of the Tweens, creating a pool of free fatty acids which are then used for lipid synthesis. Sterols were only slightly labeled in cells treated with Tweens, but accounted for nearly 50% of lipid radioactivity in cells treated with acetate. This suggested very little degradation and reutilization of the radioactive fatty acids in cells treated with Tweens. In cells treated with either [1-¹⁴C]acetate or Tween-[1-¹⁴C]-18:1, 70% of the initial fatty acid radioactivity remained in fatty acids after a 100 hour chase. By contrast, fatty acids not normally present disappeared more rapidly, suggesting differential treatment of such fatty acids compared with those normally present. Cells which had incorporated large amounts of exogenous fatty acids altered fatty acid synthesis in three distinct ways: (a) amounts of [1-¹⁴C]acetate incorporated into fatty acids were reduced; (b) cells incorporating exogenous unsaturated fatty acids increased the proportion of [1-¹⁴C]acetate partitioned into saturated fatty acids, while the converse was true of cells which had incorporated exogenous saturated fatty acids; (c) desaturation of 18:1 to 18:2 and 18:3 was reduced in cells which had incorporated unsaturated fatty acids. These results suggest that Tween-fatty acid esters will be useful for supplying fatty acids to cells for a variety of studies related to fatty acid or membrane metabolism.     

Further investigations of the incorporation of [1-14C]acetate into the lipids of the silkworm Bombyx mori L

1. After the injection of sodium [1-¹⁴C]acetate, the highest incorporation of ¹⁴C into the lipids of the silkworm was observed after 24hr. 2. The specific radioactivity of the palmitic acid fraction was greater and increased more rapidly than that of the stearic acid fraction, which was consistent with the precursor–product relationship to be expected on the basis of current concepts of fatty acid synthesis in vivo. 3. The results indicate the probability of synthesis of lipid components in tissues other than the fat body. 4. Fractionation studies indicate considerable differences in the rate of incorporation of [1-¹⁴C]acetate into neutral lipids and phospholipids between larvae and pupae as well as among tissues of larvae. 5. The rate of incorporation of [1-¹⁴C]acetate remains constant throughout pupal development.     

Removal of the acetate-moiety of 2,4-dichlorophenoxyacetic acid in Ribes sativum

Ten minutes after uptake of 2,4-dichlorophenoxyacetic acid-1-¹⁴C(2,4-D-1-¹⁴C) by excised Ribes sativum leaves, 37·8 % of the radioactivity in water-soluble metabolites was in glyoxylic acid. When 2,4-D- 2-¹⁴C was supplied under the same conditions, 23·0 % of the radioactivity of the water-soluble rnetabolites was in glyoxylic acid. Radioactive glycine and glyoxylic acid, isolated from Ribes sativum 6 hr after uptake of 2,4-D-1-¹⁴C, contained essentially all of the ¹⁴C in the carboxyl-carbon atoms. When 2,4-D-2-¹⁴C was the precursor, the glycine isolated contained 64·8 % of its radioactivity in C₂, while 60·0 % of the radioactivity in glyoxylic acid was in C₂. The side-chain label of 2,4-D-2-¹⁴C-4-³⁶Cl was more efficiently incorporated into ethanol-insoluble plant residue than the ring-label. The metabolism of glyoxylic acid-1-¹⁴C and 2,4-D-1-¹⁴C in excised Ribes sativum leaves were compared. The data suggest a cleavage of the acetate-moiety of 2,4-D resulting in a C₂ compound, perhaps glyoxylate.     

PROVENANCE OF THE ACETYL GROUP OF ACETYLCHOLINE AND COMPARTMENTATION OF ACETYL-CoA AND KREBS CYCLE INTERMEDIATES IN THE BRAIN IN VIVO

—The origin of the acetyl group in acetyl-CoA which is used for the synthesis of ACh in the brain and the relationship of the cholinergic nerve endings to the biochemically defined cerebral compartments of the Krebs cycle intermediates and amino acids were studied by comparing the transfer of radioactivity from intracisternally injected labelled precursors into the acetyl moiety of ACh, glutamate, glutamine, ‘citrate’(= citrate +cis-aconitate + isocitrate), and lipids in the brain of rats. The substrates used for injections were [1-¹⁴C]acetate, [2-¹⁴C]acetate, [4-¹⁴C]acetoacetate, [1-¹⁴C]butyrate, [1, 5-¹⁴C]citrate, [2-¹⁴C]glucose, [5-¹⁴C]glutamate, 3-hydroxy[3-¹⁴C]butyrate, [2-¹⁴C]lactate, [U-¹⁴C]leucine, [2-¹⁴C]pyruvate and [³H]acetylaspartate. The highest specific radioactivity of the acetyl group of ACh was observed 4 min after the injection of [2-¹⁴C]pyruvate. The contribution of pyruvate, lactate and glucose to the biosynthesis of ACh is considerably higher than the contribution of acetoacetate, 3-hydroxybutyrate and acetate; that of citrate and leucine is very low. No incorporation of label from [5-¹⁴C]glutamate into ACh was observed. Pyruvate appears to be the most important precursor of the acetyl group of ACh. The incorporation of label from [1, 5-¹⁴C]citrate into ACh was very low although citrate did enter the cells, was metabolized rapidly, did not interfere with the metabolism of ACh and the distribution of radioactivity from it in subcellular fractions of the brain was exactly the same as from [2-¹⁴C]pyruvate. It appears unlikely that citrate, glutamate or acetate act as transporters of intramitochondrially generated acetyl groups for the biosynthesis of ACh. Carnitine increased the incorporation of label from [1-¹⁴C]acetate into brain lipids and lowered its incorporation into ACh. Differences in the degree of labelling which various radioactive precursors produce in brain glutamine as compared to glutamate, previously described after intravenous, intra-arterial, or intraperitoneal administration, were confirmed using direct administration into the cerebrospinal fluid. Specific radioactivities of brain glutamine were higher than those of glutamate after injections of [1-¹⁴C]acetate, [2-¹⁴C]acetate, [1-¹⁴C]butyrate, [1,5-¹⁴C]citrate, [³H]acetylaspartate, [U-¹⁴C]leucine, and also after [2-¹⁴C]pyruvate and [4-¹⁴C]acetoacetate. The intracisternal route possibly favours the entry of substrates into the glutamine-synthesizing (‘small’) compartment. Increasing the amount of injected [2-¹⁴C]pyruvate lowered the glutamine/glutamate specific radioactivity ratio. The incorporation of ¹⁴C from [1-¹⁴C]acetate into brain lipids was several times higher than that from other compounds. By the extent of incorporation into brain lipids the substrates formed four groups: acetate > butyrate, acetoacetate, 3-hydroxybutyrate, citrate > pyruvate, lactate, acetylaspartate > glucose, glutamate. The ratios of specific radioactivity of ‘citrate’ over that of ACh and of glutamine over that of ACh were significantly higher after the administration of [1-¹⁴C]acetate than after [2-¹⁴C]pyruvate. The results indicate that the [1-¹⁴C]acetyl-CoA arising from [1-¹⁴C]acetate does not enter the same pool as the [1-¹⁴C]acetyl-CoA arising from [2-¹⁴C]pyruvate, and that the cholinergic nerve endings do not form a part of the acetate-utilizing and glutamine-synthesizing (‘small’) metabolic compartment in the brain. The distribution of radioactivity in subcellular fractions of the brain after the injection of [1-¹⁴C]acetate was different from that after [1, 5-¹⁴C]citrate. This suggests that [1-¹⁴C]acetate and [1, 5-¹⁴C]citrate are utilized in different subdivisions of the ‘;small’ compartment.     

Effect of pyridoxine deficiency on nucleic acid metabolism in the rat

1. The nucleic acid metabolism in the pyridoxine-deficient rat has been investigated through studies on the incorporation of radioactivity from various isotopically labelled compounds into liver and spleen DNA and RNA. 2. In pyridoxine deficiency, the incorporation of radioactivity from sodium [¹⁴C]formate was apparently increased. The magnitude of this effect on incorporation into liver RNA and DNA and spleen RNA was approximately the same. The incorporation into spleen DNA was enhanced to a much greater degree. Administration of pyridoxine 24hr. before the rats were killed reversed the changes in incorporation of radioactivity from [¹⁴C]formate. 3. In pyridoxine deficiency, the incorporation of radioactivity from dl-[3-¹⁴C]serine, [8-¹⁴C]adenine, [Me-³H]thymidine and [2-¹⁴C]deoxyuridine was decreased. The incorporation of radioactivity from l-[Me-¹⁴C]methionine was not affected. No noteworthy differences in the effect of pyridoxine deficiency on the incorporation of radioactivity from dl-[3-¹⁴C]serine into DNA and RNA were observed, whereas the effect of the deficiency on the incorporation of radioactivity from [8-¹⁴C]adenine into spleen DNA was somewhat greater than that into spleen RNA. Administration of pyridoxine 24hr. before the rats were killed reversed the changes in incorporation of radioactivity from [3-¹⁴C]serine and [8-¹⁴C]adenine. 4. The adverse effects of pyridoxine deficiency on the biosynthesis of nucleic acids and cell multiplication are discussed in relation to the role of pyridoxal phosphate in the production of C₁ units via the serine-hydroxymethylase reaction.     

Effects of dietary ethionine on methionine metabolism in a dipterous parasitoid Agria housei schwel

Metabolism of injected l-[methyl-¹⁴C]-methionine and l-[ethyl-1-¹⁴C]-ethionine was studied in female adults of Agria housei fed chemically-defined diet (control) or ethionine-supplemented diet (0.07% w/v). Flies fed ethionine-supplemented diet showed a 50% reduction in the amount of radioactivity incorporated into proteins from injected l-[methyl-¹⁴C]-methionine compared to flies fed the control diet. Small amounts of ethionine were also incorporated into proteins possibly giving rise to functionally abnormal proteins. These observations appear to explain, at least in part, the ability of ethionine to inhibit ovarian growth in A. housei. Both methionine and ethionine are oxidized to their corresponding sulphoxides; in addition to being incorporated into proteins and lipids, radioactivity was also detected in several unidentified products.     

The biosynthesis of C55 polyprenols by a cell-free preparation of Lactobacillus plantarum

A cell-free supernatant of lysates of Lactobacillus plantarum catalyses the synthesis of lipids from [2-¹⁴C]mevalonate. Of the added mevalonate, 7.5% is incorporated into lipids, which were fractionated into five components. About 4% of the radioactivity in these lipids co-chromatographs with compounds shown by mass spectrometry, n.m.r. and i.r. spectroscopy to be C₅₅ polyprenols, and about 2% co-chromatographs with a hexamer. The rest of the radioactivity is in more complex fractions. Analysis by mass spectrometry, n.m.r. and i.r. spectroscopy shows that the major C₅₅ polyprenol is undecaprenol, accompanied by an isomer containing one reduced isoprene unit. A Kuhn–Roth degradation of [¹⁴C]polyprenols indicates that the supernatant catalyses synthesis of these compounds de novo.     

INCORPORATION OF AXONALLY TRANSPORTED SUBSTANCES INTO MYELIN LIPIDS

Abstract— The possibility that axonally transported lipids and/or proteins might undergo transaxonal migration and become incorporated into surrounding myelin lamellae was studied by isolating myelin from optic tracts of myelinating rabbits at various times following intraocular injection of [3-¹⁴C]-serine and [2-³H]glycerol. Myelin isolated by a procedure employing ethylene glycol-bis(β-aminoethyl ether)-.N,N'-tetraacetic acid had relatively constant specific radioactivity with respect to both isotopes over a 21 day period. Myelin lipids showed a gradual increase in ¹⁴C specific radioactivity, attributed to reutilization of [¹⁴C]serine from the axon by a compartment of the oligodendrocyte. Free serine is postulated to arise in the axon from catabolism of axonally transported proteins (and possibly lipids) and to migrate transaxonally into the neighboring oligodendroglia. This reutilization mechanism resulted in synthesis of myelin cerebrosides, sphingomyelin, ethanolamine phosphoglycerides and possibly sulfatides, but not gangliosides or serine phosphoglycerides. The data for choline- and inositol-phosphoglycerides are inconclusive. [³H]Glycerol-labeled myelin lipids decreased slowly in ³H specific radioactivity with time, indicating either that [2-³H]glycerol does not participate in the reutilization pathway or that the label is lost in the process. Evidence is presented that ³H- and ¹⁴C-labeled lipids are true myelin constituents. Lipids from the myelin, axolemma- and axon-enriched fractions tended to converge in specific radioactivity over the 21 days, especially the former two fractions. These results together with isotope ratio changes point to an equilibration process whereby lipids are able to transfer. (or exchange) between the 3 compartments. Protein radioactivity in isolated myelin was suggested to arise from residual axon/axolemma contamination, and no evidence was found for transaxonal migration of protein into myelin. The 2 mechanisms elucidated here are believed to account for a quantitatively small portion of myelin lipid and are considered to represent a form of axon-glia interaction.     

Reserve lipid accumulation and translocation of 14C in the photosynthetically active and senescent shoot parts of Dicranum elongatum

Lipid metabolism of the subarctic moss Dicranum elongatum was studied by feeding the moss with 2-¹⁴C-acetate and, after extraction of the lipids, counting the ¹⁴C-content of different lipid fractions immediately after feeding or after chase periods. Translocation of ¹⁴C after ¹⁴C-feeding was studied with autoradiography. Both low temperature (+6°C) and drought (at +23°C) resulted in increased incorporation of ¹⁴C into the neutral lipid (NL) fraction and decreased incorporation of ¹⁴C into the glycolipid (GL) fraction of the green shoot part of the moss. The distribution of radioactivity between the NL classes suggests that diacylglycerols (1, 2-DAG) and common triacylglycerols (cTAG) are turned into acetylenic triacylglycerols (aTAG), which are accumulated preferentially. The decrease in the radioactivity of the GL fraction was due to two unknown fractions, whereas ¹⁴C incorporation into the chloroplast membrane lipids, monogalactosyl diacylglycerol (MGDG) and digalactosyl diacylglycerol (DGDG), was very low throughout the experiments. The phospho-lipid (PL) fraction accounted for 48–63% of total lipid radioactivity at both low and high temperatures. 2-¹⁴C-acetate feeding to the senescent moss part resulted in vigorous ¹⁴C incorporation into the lipids, especially into the reserve TAGs. Electron microscopic examination showed the presence of plastids, which explains the capability of the senescent part of the moss for lipid synthesis. The fact that transport of ¹⁴C from 2-¹⁴C-acetate took place upwards and downwards in the moss shoot, together with the capability for lipid synthesis of the senescent moss part, supports the suggestion that the senescent moss part plays a role as an energy store.     

Effects of desmethylimipramine and diphenylpropene derivatives on synthesis of rat brain lipids in vivo

The effects of antidepressant compounds on the synthesis of brain lipids from [1-¹⁴C] acetate $\text{in vivo}$ in 15 day old rats have been investigated. Compounds used included the drug desmethylimipramine (DMI), the tetrabenazine antagonist 3-methylamino-1:1-diphenylprop-1-ene (II) and the primary (I) and tertiary (III) amine analogues of (II). Compound (II), the most potent tetrabenazine antagonist in the diphenylpropene series, significantly increased lipogenesis, whereas the remaining compounds did not. The results from fractionation of the lipid extract from rats treated with (II) indicated that the incorporation of radioactivity from [1-¹⁴C] acetate increased proportionally in all neutral lipids and phospholipids. Tetrabenazine also increased brain lipogenesis $\text{in vivo}$ and altered the distribution within lipid classes of radioactivity from [1-¹⁴C] acetate. Using [¹⁴C] labelled compound, the concentration of (II) in the brain under the present experimental conditions has been determined.     

Occurrence of acetylcholine-hydrolyzing activity at the stele-cortex interface

Acetylcholine (ACh) is a chemical transmitter serving to propagate an electrical perturbation across the synaptic junctions of animals. ACh and AChE have previously been demonstrated to occur in plants. In this work, we detected AChE at the interface between stele and cortex of the mesocotyl of Zea mays by measuring hydrolysis of acetylthiocholine and by liberation of labeled acetate from [1-¹⁴C]ACh. AChE activity was also detected in a crude membrane fraction. The hydrolytic activity is inhibited by neostigmine. Hydrolysis of ACh was also measured after injection of [1-¹⁴C]ACh into kernels of Zea mays and the radioactivity transported into the mesocotyl cortex. A gravity stimulus was then given by placing the plants in a horizontal position. Significantly more radioactivity was found in the lower cortex of horizontally placed seedlings. A working hypothesis is presented for the involvement of ACh and AChE in the tropic response of Z. mays seedlings.     

Incorporation of labelled glycerols into ether lipids in Caldariella acidophila

The lipids of Caldariella acidophila, an extreme thermophile member of the new archaebacteria group, are macrocyclic tetraethers. They are made up of two glycerol molecules (or one glycerol and one nonitol) bridged through ether linkages by two C₄₀16,16′-biphytanyl chains. To elucidate the biosynthesis of the glycerol moiety of these tetraethers and the mechanism of glycerol ether assembly, labelled [U-¹⁴C, 1(3)-³H]glycerol and [U-¹⁴C, 2-³H]glycerol, were fed to C. acidophila. Both precursors were selectively incorporated with high efficiency, and without any change in the ³H/¹⁴C ratio, in the glycerol moiety of tetraethers. These results suggest that the ether forming step in the biosynthesis of tetraether lipids of C. acidophila, occurs without any loss of hydrogen from any of the glycerol carbons which in turn could be directly alkylated by geranylgeranyl pyrophosphate. The incorporation of radioactivity in the isoprenoid chains and into nonitol is also analysed.     

Metabolism of tyramine and feruloyltyramine in TMV inoculated leaves of Nicotiana tabacum

TMV inoculation is known to stimulate tyramine N-feruloyl-CoA transferase activity in Nicotiana tabacum cv Xanthi n.c. leaves during the hypersensitive reaction. When [2-¹⁴C]-tyramine is fed for 2 hr to TMV inoculated leaf discs or detached leaves, ca 1 % of the supplied radioactivity is integrated into cinnamoyl-, p-coumaroyl- and feruloyltyramine and up to 14 % is integrated into the cell wall residue. [2-¹⁴C]-tyramine can only be partially released from this residue by acid hydrolysis. After nitrobenzene oxidation, 97 % of the radioactivity found in the cell walls is made soluble but only 13 % is recovered in p-hydroxybenzaldehyde. Feruloyltyramine is very rapidly metabolised, ca 20 % of the administrated radioactivity is found after 2 hr feeding in unindentified methanoi soluble metabolites. Acid hydrolysis of the cell wall fraction, which hydrolyses the amide bond of feruloyltyramine, releases labelled tyramine, while radioactivity is still detected in the acid insoluble residue. Label from [¹⁴C]-feruloyltyramine is integrated into this residue more quickly than from free [2-¹⁴C]-tyramine.     

Incorporation of palmitic acid-1-14C into lipids of pharate adult tissues of Bombyx mori

Incorporation of palmitic acid-1-¹⁴C into pharate adult tissues and their lipid components of Bombyx mori was investigated. Rapid incorporation of radioactivity took place predominantly in fat body and haemolymph lipids, and partially in ovarian lipids immediately after the injection at the middle stage of pharate adult development. The major parts of the radioactivities in fat body, haemolymph and ovary were distributed in triglycerides and phospholipids, diglycerides, and triglycerides, respectively. The patterns of time course of incorporation of radioactivity into lipid components of pharate adult tissues suggest that the major form of lipid released from fat body may be diglycerides and the diglycerides in haemolymph are probably the main source of ovarian triglycerides.     

Metabolism of Linoleic Acid or Mevalonate and 6-Pentyl-α-Pyrone Biosynthesis by Trichoderma Species

The understanding of the biosynthetic pathway of 6-pentyl-α-pyrone in Trichoderma species was achieved by using labelled linoleic acid or mevalonate as a tracer. Incubation of growing cultures of Trichoderma harzianum and T. viride with [U-¹⁴C]linoleic acid or [5-¹⁴C]sodium mevalonate revealed that both fungal strains were able to incorporate these labelled compounds (50 and 15%, respectively). Most intracellular radioactivity was found in the neutral lipid fraction. At the initial time of incubation, the radioactivity from [¹⁴C]linoleic acid was incorporated into 6-pentyl-α-pyrone more rapidly than that from [¹⁴C]mevalonate. No radioactivity incorporation was detected in 6-pentyl-α-pyrone when fungal cultures were incubated with [1-¹⁴C]linoleic acid. These results suggested that β-oxidation of linoleic acid was a probable main step in the biosynthetic pathway of 6-pentyl-α-pyrone in Trichoderma species.     

Accessibility of glucose 6-phosphate: phosphohydrolase to antibody attack in modified microsomal vesicles

Upon subcellular fractionation of (murine) Friend erythroleukaemic cells (FELCs), purified plasma membranes were identified by their high enrichment in specific marker enzymes and typical plasma membrane lipids. When FELCs were incubated for short periods with ³²P_i before cell fractionation, the lipid-bound radioactivity was almost exclusively present in phosphatidylinositol-4-phosphate (DPI) and phosphatidylinositol-4,5-bisphosphate (TPI), and its distribution closely matched that of the plasma membrane markers. In addition, purified plasma membranes actively incorporated ³²P from [γ-³²P]ATP into polyphosphoinositides, and the specific activities of the involved kinases were again mostly enriched in the plasma membrane fraction.     

Alkaline decomposition of d-xylose-1-C, d-glucose-1-C, and d-glucose-6-C

The distribution of radioactivity in the three- and four-carbon saccharinic acids, lactic acid and 2,4-dihydroxybutyric acid, obtained from d-xylose-1-¹⁴C, d-glucose-1-¹⁴C, and d-glucose-6-¹⁴C, was measured. The relative importance of the various mechanisms for forming 2,4-dihydroxybutyric acid was determined. Recombination of two-carbon fragments was found to be an important mechanism at the high alkalinity and temperature employed.     

Lipid Composition and Metabolism of Volvox carteri

The membrane structural lipids of somatic cells and gonidia isolated from Volvox carteri f. nagariensis spheroids have been characterized. The principal polar lipid components of both cell types are sulfoquinovosyl diglyceride, mono- and digalactosyl diglyceride, phosphatidylglycerol, phosphatidylethanolamine, and 1(3), 2-diacylglyceryl-(3)-O-4′-(N,N,N,-trimethyl)homoserine. Light-synchronized cultures of spheroids were shown to incorporate [¹⁴C]bicarbonate, [³⁵S]sulfate, [¹⁴C]palmitic acid, and [¹⁴C]lauric acid into complex lipids. [¹⁴C]Palmitic acid was incorporated mainly into diacylglyceryltrimethylhomoserine and was not significantly modified by elongation or desaturation. In contrast, [¹⁴C]lauric acid was incorporated into a wider variety of complex lipids and was also converted into longer chain saturated and unsaturated fatty acids. Volvox is a promising system for studying the role of membranes in algal cellular differentiation.