Relationship between specific dynamic action and protein deposition in calanoid copepods

The link between specific dynamic action (SDA) and protein deposition was investigated in copepodites stage V of two calanoid copepod species, the neritic Acartia tonsa and the oceanic Calanus finmarchicus. This was done by measuring respiration before, during, and after a specific feeding period and measuring the incorporation of carbon into proteins. These were also measured on individuals incubated with cycloheximide, an antibiotic that inhibits protein synthesis. The cycloheximide treatment significantly diminished the magnitude of SDA in both A. tonsa and C. finmarchicus, and inhibited carbon incorporation into protein in both species. This provides evidence that the rate at which protein deposition takes place greatly affects the magnitude of SDA. The specific respiration rates of both starving and feeding copepods were generally higher in A. tonsa than in C. finmarchicus. This influenced SDA, the magnitude of SDA normalised to an 8 h feeding period being threefold higher in A. tonsa (78.7+/-25.7 nlO(2) μgC(-1)) than in C. finmarchicus (27.5+/-11.6 nlO(2) μgC(-1)). This difference may arise due to differences in energy allocation in the organisms of the copepodite V stage of the two species. In this stage C. finmarchicus deposits large quantities of storage lipids, predominately wax esters, whereas A. tonsa deposits proteins during somatic growth.     

Influence of two different green algal diets on specific dynamic action and incorporation of carbon into biochemical fractions in the copepod Acartia tonsa

Previous studies have shown that the two green algae Tetraselmissp. (Prasinophyceae) and Dunaliella tertiolecta (Chlorophyceae)induce high and low egg production rates in Acartia tonsa. Theprimary goal of the present study was to investigate if thisis attributable to differences in the specific dynamic action(SDA) of the two diets. Secondly, we wanted to investigate ifany qualitative differences in the incorporation of nutritionalconstituents from the two diets are influencing SDA. The functionalresponse of ingestion was very different with the two diets.Ingestion of T. impellucida was relatively high even at lowfood concentrations with a maximum of 19 µg C ind^-1 day^-1.The functional response was more clearly sigmoidal on D. tertiolectawith a maximum of 7.3 µg C ind^-1 day^-1. The higher ingestionrate of T. impellucida also induced higher respiration rates.Maximum respiration rates were 3.0 nl O₂ ind^-1 min^-1 on T. impellucidaand 1.5 nl O₂ ind^-1 min^-1 onD. tertiolecta. This created significantlydifferent SDA coefficients: 0.19 on T. impellucida and 0.06on D. tertiolecta, which implies that the magnitude of SDA isstrongly influenced by the composition of the diet. The incorporationof carbon into lipids was significantly higher on D. tertiolecta.However, because of lack of longer chain fatty acids in D. tertiolectathe copepods did not benefit from this. Thus, the proportionof carbon allocated to egg lipids was much lower than when feedingon T. impellucida. Acartia tonsa incorporated relatively morecarbon into proteins when feeding on T. impellucida than onD. tertiolecta. Since protein synthesis is energetically verydemanding this is probably the reason for the higher SDA coefficientin those feeding on T. impellucida.     

Fatty acid metabolism by a particulate fraction from germinating peas

The incorporation of fatty acids into lipid fractions was studied using a high-speed particulate fraction from germinating peas (Pisum sativum cv Feltham First). The acids were incorporated principally into the acyl-CoA and polar lipid fractions, with unsaturated fatty acids labelling the latter fraction at higher rates than saturated substrates. α-Hydroxylation also occurred. Oleate from oleoyl-CoA or oleoyl-acyl carrier protein was incorporated into polar lipids faster than from ammonium oleate. The incorporation of fatty acids into polar lipids was dependent on the presence of CoA and ATP in the medium and on the consequent generation of acyl-CoA's. Time-course studies and experiments when two fatty acid substrates were added consecutively confirmed the role of acyl-CoA's in the transfer of acyl groups to phospholipids. Although CoA was necessary when acyl-CoA's had to be generated, high concentrations were found to inhibit the rate ofacyl transfer. The results are discussed in terms ofthe ‘witching mechanism’ for controlling the fate of fatty acids in the plant cell.     

Diel Variations in Carbon Metabolism by Green Nonsulfur-Like Bacteria in Alkaline Siliceous Hot Spring Microbial Mats from Yellowstone National Park

Green nonsulfur-like bacteria (GNSLB) in hot spring microbial mats are thought to be mainly photoheterotrophic, using cyanobacterial metabolites as carbon sources. However, the stable carbon isotopic composition of typical Chloroflexus and Roseiflexus lipids suggests photoautotrophic metabolism of GNSLB. One possible explanation for this apparent discrepancy might be that GNSLB fix inorganic carbon only during certain times of the day. In order to study temporal variability in carbon metabolism by GNSLB, labeling experiments with [¹³C]bicarbonate, [¹⁴C]bicarbonate, and [¹³C]acetate were performed during different times of the day. [¹⁴C]bicarbonate labeling indicated that during the morning, incorporation of label was light dependent and that both cyanobacteria and GNSLB were involved in bicarbonate uptake. ¹³C-labeling experiments indicated that during the morning, GNSLB incorporated labeled bicarbonate at least to the same degree as cyanobacteria. The incorporation of [¹³C]bicarbonate into specific lipids could be stimulated by the addition of sulfide or hydrogen, which both were present in the morning photic zone. The results suggest that GNSLB have the potential for photoautotrophic metabolism during low-light periods. In high-light periods, inorganic carbon was incorporated primarily into Cyanobacteria-specific lipids. The results of a pulse-labeling experiment were consistent with overnight transfer of label to GNSLB, which could be interrupted by the addition of unlabeled acetate and glycolate. In addition, we observed direct incorporation of [¹³C]acetate into GNSLB lipids in the morning. This suggests that GNSLB also have a potential for photoheterotrophy in situ.     

Malate- and pyruvate-dependent Fatty Acid synthesis in leucoplasts from developing castor endosperm

Leucoplasts were isolated from the endosperm of developing castor (Ricinis communis) endosperm using a discontinuous Percoll gradient. The rate of fatty acid synthesis was highest when malate was the precursor, at 155 nanomoles acetyl-CoA equivalents per milligram protein per hour. Pyruvate and acetate also were precursors of fatty acid synthesis, but the rates were approximately 4.5 and 120 times less, respectively, than when malate was the precursor. When acetate was supplied to leucoplasts, exogenous ATP, NADH, and NADPH were required to obtain maximal rates of fatty acid synthesis. In contrast, the incorporation of malate and pyruvate into fatty acids did not require a supply of exogenous reductant. Further, the incorporation of radiolabel into fatty acids by leucoplasts supplied with radiolabeled malate, pyruvate, or acetate was reduced upon coincubation with cold pyruvate or malate. The data suggest that malate and pyruvate may be good in vivo sources of carbon for fatty acid synthesis and that, in these preparations, leucoplast fatty acid synthesis may be limited by activity at or downstream of the acetyl-CoA carboxylase reaction.     

Effects of acclimation and acute temperature change on specific dynamic action and gastric processing in the green shore crab, Carcinus maenas

The effects of temperature acclimation and acute temperature change were investigated in postprandial green shore crabs, Carcinus maenas. Oxygen uptake, gut contractions and transit rates and digestive efficiencies were measured for crabs acclimated to either 10 °C or 20 °C and subsequently exposed to treatment temperatures of 5, 15, or 25 °C. Temperature acclimation resulted in a partial metabolic compensation in unfed crabs, with higher oxygen uptake rates measured for the 10 °C acclimated group exposed to acute test temperatures. The Q₁₀ values were higher than normal, probably because the acute temperature change prevented crabs from fully adjusting to the new temperature. Both the acclimation and treatment temperature altered the characteristics of the specific dynamic action (SDA). The duration of the response was longer for 20 °C acclimated crabs and was inversely related to the treatment temperature. The scope (peak oxygen consumption) was also higher for 20 °C acclimated crabs with a trend towards an inverse relationship with treatment temperature. Since the overall SDA (energy expenditure) is a function of both duration and scope, it was also higher for 20 °C acclimated crabs, with the highest value measured at the treatment temperature of 15 °C. The decline in total SDA after acute exposure to 5 and 25 °C suggests that both cold stress and limitations to oxygen supply at the temperature extremes could be affecting the SDA response. The contractions of the pyloric sac of the foregut region function to propel digesta through the gut, and contraction rates increased with increasing treatment temperature. This translated into faster transit rates with increasing treatment temperatures. Although pyloric sac contractions were higher for 20 °C acclimated crabs, temperature acclimation had no effect on transit rates. This suggests that a threshold level in pyloric sac contraction rates needs to be reached before it manifests itself on transit rates. Although there was a correlation between faster transit times and the shorter duration of the SDA response with increasing treatment temperature, transit rates do not make a good proxy for calculating the SDA characteristics. The digestive efficiency showed a trend towards a decreasing efficiency with increasing treatment temperature; the slower transit rates at the lower treatment temperatures allowing for more efficient nutrient absorption. Even though metabolic rates of 10 °C acclimated crabs were higher, there was no effect of acclimation temperature on digestive efficiency. This probably occurred because intracellular enzymes and digestive enzymes are modulated through different control pathways. These results give an insight into the metabolic and digestive physiology of Carcinus maenas as it makes feeding excursions between the subtidal and intertidal zones.     

Synthesis of acyl-CoAs by isolated spinach chloroplasts in relation to added CoA and ATP

The kinetics of incorporation of [2-¹⁴C] acetate into lipids and acyl-CoAs in relation to added CoA and ATP by isolated spinach chloroplasts have been examined. The effect of the concentration of these cofactors on lipid and acyl-CoA synthesis was also studied. In the absence of cofactors, or when only one was present, the incorporation was very low and went mainly into lipids. When both cofactors were present a strong stimulation of both activities occurred. After 25 min, acyl-CoAs were more strongly labeled than lipids and both activities continued linearly for at least 60 min.Abbreviations ACP acyl carrier protein - FFA free fatty acids     

Yeast and cancer cells – common principles in lipid metabolism

One of the paradigms in cancer pathogenesis is the requirement of a cell to undergo transformation from respiration to aerobic glycolysis – the Warburg effect – to become malignant. The demands of a rapidly proliferating cell for carbon metabolites for the synthesis of biomass, energy and redox equivalents, are fundamentally different from the requirements of a differentiated, quiescent cell, but it remains open whether this metabolic switch is a cause or a consequence of malignant transformation. One of the major requirements is the synthesis of lipids for membrane formation to allow for cell proliferation, cell cycle progression and cytokinesis. Enzymes involved in lipid metabolism were indeed found to play a major role in cancer cell proliferation, and most of these enzymes are conserved in the yeast, Saccharomyces cerevisiae. Most notably, cancer cell physiology and metabolic fluxes are very similar to those in the fermenting and rapidly proliferating yeast. Both types of cells display highly active pathways for the synthesis of fatty acids and their incorporation into complex lipids, and imbalances in synthesis or turnover of lipids affect growth and viability of both yeast and cancer cells. Thus, understanding lipid metabolism in S. cerevisiae during cell cycle progression and cell proliferation may complement recent efforts to understand the importance and fundamental regulatory mechanisms of these pathways in cancer.     

Carbon balance and energetics of cyooprotectant synthesis in a freeze-tolerant insect: responses to perturbation by anoxia

Summary The capacity for polyol synthesis by larvae of Eurosta solidaginis was evaluated under aerobic versus anoxic (N₂ gas atmosphere) conditions. Glycerol production occurred readily in aerobic larvae at 13°C. Under anoxic conditions, however, net glycerol accumulation was only 57% of the aerobic value after 18 d, but the total hydroxyl equivalents available for cryoprotection were balanced by the additional synthesis of sorbitol. The efficiency of carbon conversion to polyols was much lower in anaerobic larvae. The ATP requirement of glycerol biosynthesis necessitated a 22% greater consumption of carbohydrate, when anaerobic and resulted in the accumulation of equimolar amounts of l-lactate and l-alanine as fermentative end products. The ratio of polyols produced to glycolytic end products formed was consistent with the use of the hexose monophosphate shunt to generate the reducing equivalents needed for cryoprotectant synthesis. A comparable experiment analyzed sorbitol synthesis at 3°C under aerobic versus anoxic conditions. Sorbitol synthesis was initiated more rapidly in anaerobic larvae, and the final sorbitol levels attained after 18 d were 60% higher than in aerobic larvae. The enhanced sorbitol output under anoxia may be due to an obligate channeling of a high percentage of total carbon flow through the hexose monophosphate shunt at 3°C. Carbon processed in this way generates NADPH which, along with the NADH output of glycolysis, must be reoxidized if anaerobic ATP synthesis is to continue. Redox balance within the hexose monophosphate shunt is maintained through NADPH consumption in the synthesis of sorbitol.     

Storage and mobilisation of nutriment for uterine milk synthesis by Glossina morsitans

Nitrogen content of eggs and larvae of Glossina morsitans was a constant proportion of dry weight and equivalent to ca. 55% protein assuming tsetse proteins contain 16% nitrogen. The larval gut content (uterine milk) contained 40% protein. Fatty acid composition of lipids in the milk and in the larval body was similar, with Palmitic (35–38%), Palmitoleic (31–35%) and Oleic acid (23–25%) predominating. Results support the hypothesis that uterine milk contains both protein and lipid and that its composition is relatively constant throughout the period of its synthesis and secretion.Patterns of incorporation of radioactivity by fertilized adult females from injected [¹⁴C]-leucine changed throughout a pregnancy cycle. High levels of incorporation into lipid (22–30%) during early pregnancy fell to around 10% during late pregnancy. Over the same period low levels of incorporation into protein (5%) increased to 15%. Results support the hypothesis that uterine milk is synthesized from a lipid store laid down in early pregnancy coupled with protein derived largely from blood meals ingested later. Such a system would not require the insect to store proteins for larval growth and is economical in terms of energy expenditure.     

Ovarian maturation in Leucophaea maderae: Juvenile hormone regulation of thymidine uptake into follicle cell DNA

Our research demonstrates that juvenile hormone (JH I) stimulates thymidine incorporation into ovarian follicle cell DNA in the ovoviviparous cockroach, Leucophaea maderae.A rapid, quantitative method for monitoring ³H-thymidine incorporation into ovarian DNA, in vitro, is described. Cultured ovarian tissue from L. maderae incorporates ³H-thymidine into DNA at a linear rate between 16 and 120 min; analysis of the incorporated label revealed at least 98% of it to be in DNA.Using L. maderae females that had been mated 7 days after adult emergence, we monitored the following biochemical phenomena during the 18–22 day period of terminal oöcyte growth: (1) ³H-thymidine incorporation into ovarian DNA: (2) general protein synthesis in fat body; and (3) specific fat body vitellogenin synthesis.Decapitation of mated females with maturing oöcytes arrested both ovarian DNA synthesis and fat body vitellogenin synthesis. Substantial restoration of both types of synthesis was induced by injection of JH I. The resumption of thymidine incorporation into DNA was localized in the follicular epithelium of the terminal oöcyte.In decapitated virgin females, injection of JH I stimulated oöcyte growth and ³H-thymidine incorporation into ovarian DNA. Dose and time response curves indicate that peak stimulation of ovarian DNA synthesis occurred between 72 and 96 hr after administration of a single optimal dose of 25 μg JH I. The concurrent manifestation of ³H-thymidine uptake into ovarian DNA and activity within the fat body indicates that a similar hormonal mode of action may be operative with respect to both tissue types in virgin females.     

Use of carbon sources for lipid biosynthesis in Mycobacterium leprae: a comparison with other pathogenic mycobacteria

Carbon from glycerol and palmitate, but not significantly from five other carbon sources tested, was incorporated into lipids by suspensions of non-growing Mycobacterium leprae organisms. However, of the five other substrates three-citrate, glucose and pyruvate-were taken up. Nongrowing Mycobacterium microti and Mycobacterium avium incorporated carbon into lipids from most simple carbon sources tested unless they were obtained from growth media including palmitate or from experimentally infected animals, when incorporation of carbon into lipids from carbon sources except palmitate occurred up to 20 times more slowly. Thus, utilization of simple carbon appeared to be repressible while utilization of the one fatty acid tested, palmitate, appeared constitutive. In M. leprae, carbon from glycerol was incorporated into the glycerol moiety of acylglycerols but not into the fatty acid moieties or into free fatty acids. M. microti and M. avium incorporated carbon from simple carbon sources into fatty acids, even (though very slowly) when these organisms were obtained from host tissue. Isocitrate lyase, malate synthase and acetate kinase were detected in M. leprae. However acetyl-CoA synthetase was not detectable and phosphoacetylase was deficient; thus, M. leprae may be incapable of making acetyl-CoA from acetate. Phosphotransacetylase was readily detected in both host-grown M. avium and M. microti.     

Palmitate incorporation into lipids by lung subcellular fractions

The incorporation of palmitate into lipids by hamster lung subcellular fractions was examined and compared to the simultaneous incorporation of sn-glycero-3-phosphate. The rate of incorporation was greater for the microsomal fraction than for the mitochondria-rich fraction with very little incorporation by the supernatant. The supernatant, however, increased the rate of incorporation by 60–70% when added to the particulate fractions. The presence of CoA, ATP and rac-glycerophosphate in the incubation medium was required for optimal incorporation in all fractions. Comparison of incorporation of sn-glycero-3-phosphate and palmitate into lipids indicated that a great part of palmitate incorporation into 3-sn-phosphatidylcholine did not proceed via the diglyceride pathway. The highest de novo incorporation of palmitate was observed into 3-sn-phosphatidylethanolamine.     

Biochemical content, energy composition and reproductive effort in the broadcasting sea star Asterias vulgaris over the spawning period

To assess sex differences in reproductive effort, we examined the biochemical composition and energetic content of the principal body components of the broadcast spawning sea star Asterias vulgaris in the Mingan Islands in the northern Gulf of St. Lawrence, eastern Canada. The body wall was the most stable body component, showing no variations in mass or in lipid and protein content (and total energetic content) between sexes or during spawning. Patterns in the gonads differed between sexes and with spawning. The lipid, protein and carbohydrate content of the ovary dropped during spawning, while only the protein content of the testis decreased significantly. Reproductive effort, expressed as loss of energy in the gonads during spawning for an individual weighing 10 g in underwater mass (8.2 cm in radius), was six times greater in females (49.5 kJ) than males (7.9 kJ). The energetic content of the pyloric caeca also decreased during spawning, by 17.7 kJ in females and 21.5 kJ in males, mainly due to a decrease in lipids. If this decrease is included as reproductive effort, it lessens the gender difference. The caecum decrease possibly represented expenditures due to formation of aggregations or the expulsion of gametes during spawning. Effectively, we observed aggregations during a massive spawning in this population. The sex ratio did not differ from 1:1 in all size classes sampled. This suggests that, unless males suffer higher mortality, females manage to allocate as much energy to somatic growth as males, possibly by feeding at higher rates to compensate for their higher reproductive effort. Stomach protein content tended to be higher in females than males and may indicate greater muscular development to facilitate digestion.     

Ketone-body utilization and lipid synthesis by developing rat brain—a comparison between in vivo and in vitro experiments

The distribution of ketone bodies between oxidation and lipid synthesis was analysed in homogenates of developing rat brain. The capacity for lipid synthesis of homogenized or minced brain preparations was compared with rates of lipid synthesis in vivo, assessed by incorporation of ³H from ³H₂O into fatty acids and cholesterol. Brain homogenates of suckling rats (but not those of adults) incorporated label from [3-¹⁴C]ketone bodies into lipids, but this process was slow as compared to ¹⁴CO₂ production (< 5%) and much slower than the total rate of ketone-body utilization (< 0.5%). Study of ³H₂O incorporation demonstrated that the rates of lipogenesis and cholesterogenesis are at least one order of magnitude higher in vivo than in vitro. Maximal rates of ³H incorporation into fatty acids (3 μmol/g brain . h) and into cholesterol (0.6 μmol/g brain . h) were found during the third postnatal week. Adult rats still incorporated ³H into brain fatty acids at an appreciable rate (1 μmol/g brain . h), whereas cholesterogenesis was very low. It is concluded that in vitro measurements of lipid synthesis severely underestimate the rates that occur in developing rat brain in vivo. The high rate of ³H incorporation into lipids by developing and adult rat brain as compared to the amounts of these lipids present in the brain suggests an important contribution of endogenous lipid synthesis during brain development and an appreciable rate of fatty acid turnover during brain growth, but also in the adult brain.     

A cell-free approach to the study of membrane trafficking in frozen rat brains potentially applicable to frozen autopsy material

Summary A cell-free transfer system was used to measure capacity of brain membranes to support membrane renewal. To study transfer in brain, radiolabeled donor microsome fractions were prepared using brain slices from rats or frozen human brain autopsy specimens. Acceptor fractions, prepared from fresh or frozen rat brain or frozen human brain autopsy specimens, were immobilized on nitrocellulose. The complete reconstituted transfer system contained ATP plus ATP-regenerating system (or NADH) as a source of energy and brain cytosol. Slices of frozen brain incorporated acetate into membrane lipids with approximately the same efficiency as fresh brains. This efficiency declined with storage at 4 °C but only slowly. Donor fractions labeled with acetate from frozen slices exhibited specific transfer (37 °C minus 4 °C) of labeled membrane lipids with efficiencies comparable to fresh. The acceptor fraction could be prepared either from fresh or frozen material. Transfer was on the average two-fold stimulated by ATP at 37 °C compared to no ATP. Transfer also was stimulated by NADH. Analysis of linear transfer rates between 0 and 30 min revealed no significant effect of delay time or of time of prolonged storage on transfer efficiency beyond an initial decline of ca. 25% observed within the first two weeks after freezing. A decline of transfer was obtained with brains as the animals aged.     

Effect of meal size on the specific dynamic action of the juvenile snakehead (Channa argus)

The effect of meal size on the specific dynamic action (SDA) of the juvenile snakehead (Channa argus) was assessed at 25 °C. The fish were fed with test diets at meal sizes of 0.5, 1, 2, 3, 4, and 5% body mass and the postprandial oxygen consumption rate was determined at 1-h intervals until it returned to the pre-prandial level. The peak metabolic rate increased from 237.4 to 283.2 mg O₂ kg^− 1 h^− 1 as the relative meal size increased from 0.5% to 3% and leveled off at 4% and 5%. Factorial metabolic scope increased from 1.53 to 1.99 and SDA duration increased from 11.7 to 32.3 h as the relative meal size increased from 0.5% to 5%. The relationship between SDA duration (D) and relative meal size (M) was described as: D = 4.28 M + 10.62 (r² = 0.752, P < 0.05, n = 50). The energy expended on SDA increased while the SDA coefficient decreased with increasing meal size. The results of the present study suggest that the snakehead may adopt different feeding strategies when taking in different amounts of food.     

Diel variations in carbon metabolism by green nonsulfur-like bacteria in alkaline siliceous hot spring microbial mats from Yellowstone National Park

Green nonsulfur-like bacteria (GNSLB) in hot spring microbial mats are thought to be mainly photoheterotrophic, using cyanobacterial metabolites as carbon sources. However, the stable carbon isotopic composition of typical Chloroflexus and Roseiflexus lipids suggests photoautotrophic metabolism of GNSLB. One possible explanation for this apparent discrepancy might be that GNSLB fix inorganic carbon only during certain times of the day. In order to study temporal variability in carbon metabolism by GNSLB, labeling experiments with [13C]bicarbonate, [14C]bicarbonate, and [13C]acetate were performed during different times of the day. [14C]bicarbonate labeling indicated that during the morning, incorporation of label was light dependent and that both cyanobacteria and GNSLB were involved in bicarbonate uptake. 13C-labeling experiments indicated that during the morning, GNSLB incorporated labeled bicarbonate at least to the same degree as cyanobacteria. The incorporation of [13C]bicarbonate into specific lipids could be stimulated by the addition of sulfide or hydrogen, which both were present in the morning photic zone. The results suggest that GNSLB have the potential for photoautotrophic metabolism during low-light periods. In high-light periods, inorganic carbon was incorporated primarily into Cyanobacteria-specific lipids. The results of a pulse-labeling experiment were consistent with overnight transfer of label to GNSLB, which could be interrupted by the addition of unlabeled acetate and glycolate. In addition, we observed direct incorporation of [13C]acetate into GNSLB lipids in the morning. This suggests that GNSLB also have a potential for photoheterotrophy in situ.     

Phosphatidylcholine and sphingomyelin containing an elaidoyl fatty acid can form cholesterol-rich lateral domains in bilayer membranes

Elaidic acid is a trans-fatty acid found in many food products and implicated for having potentially health hazardous effects in humans. Elaidic acid is readily incorporated into membrane lipids in vivo and therefore affects processes regulating membrane physical properties. In this study the membrane properties of sphingomyelin and phosphatidylcholine containing elaidic acid (N-E-SM and PEPC) were determined in bilayer membranes with special emphasis on their interaction with cholesterol and participation in ordered domain formation. In agreement with previous studies the melting temperatures were found to be about 20 °C lower for the elaidoyl than for the corresponding saturated lipids. The trans-unsaturation increased the polarity at the membrane-water interface as reported by Laurdan fluorescence. Fluorescence quenching experiments using cholestatrienol as a probe showed that both N-E-SM and PEPC were incorporated in lateral membrane domains with sterol and saturated lipids. At low temperatures the elaidoyl lipids were even able to form sterol-rich domains without any saturated lipids present in the bilayer. We conclude from this study that the ability of N-E-SM and PEPC to form ordered domains together with cholesterol and saturated phospho- and sphingolipids in model membranes indicates that they might have an influence on raft formation in biological membranes.     

Incorporation of14C-radioactivity into various lipid classes at different growth-stages of culturedLaminaria japonica

A study is reported on the incorporation of¹⁴C-acetate into lipid classes from three different growth stages ofLaminaria japonica, a species long used for food in Japan. This was done because of the possible utilization of its lipids.Radioactivity incorporated into whole lipids in the three growth stages under the same experimental conditions (10 °C, 500 lux) increased with maturity of the thalli. The radioactivity was found mainly in PC, TG and 1,2-DG and subsequently distributed into other lipid classes (PG,PI,PE,MGDG,SQDG and DGDG) to a lesser extent. The incorporation patterns of the former group were similar at all stages, but those of the latter group differed slightly according to growth stage.In juvenile thalli,¹⁴C was incorporated to a much higher extent into PG, MGDG, PI and fucosterol than PE, SQDG, DGDG and MG, while the¹⁴C-incorporation into MG, SQDG, DGDG and PS in the mature growth stage was higher than into the other lipid classes. The absolute level of incorporation was higher for all these compounds in mature thalli than the thalli of other growth stages.