Isolation and Characterization of a Δ5-Desaturase from Oblongichytrium sp.

We isolated a cDNA clone with homology to known desaturase genes from Oblongichytrium sp., recently classified as a new genus of thraustochytrids (Labyrinthulomycetes), and found that it encoded Δ5-desaturase by its heterologous expression in yeast. The enzyme had higher activity toward 20:4n-3 than 20:3n-6, indicating that this Δ5-desaturase can be used in the production of n-3 polyunsaturated fatty acids in transgenic organisms.     

Docosahexaenoate-containing phospholipids in sarcoplasmic reticulum and retinal photoreceptors. A proposal for a role in Ca2+-ATPase calcium transport

A critical review of the experimental literature concerning the metabolism of all-cis-4, 7, 10, 13, 16, 19-docosahexaenoate-containing phospholipids in muscle and retina suggests that it plays an essential role in maximizing the Ca²⁺/ATP stoichiometry of the Ca²⁺-ATPase of sarcoplasmic reticulum and retinal photoreceptor disks. Docosahexaenoate-phosphatidylcholine is proposed to participate in oligomerization of Ca²⁺-ATPase necessary for the establishment of a high Ca²⁺/ATP coupling ratio of the Ca²⁺ pump in these tissues. Possible tests of this hypothesis are presented.     

Dietary fat influences electric membrane properties of neurons in cell culture

1. SJL/J mice were maintained on semipurified diets which differed in the ratio of polyunsaturated/saturated fatty acid content (P/S). Exposure was from conception and was maintained for periods ranging from 6 to 34 weeks. 2. Neural cell cultures were prepared from dorsal root ganglia (DRG). After 6 and 20 days of culture, neuronal electric membrane properties were determined quantitatively by intracellular recording. 3. A number of significant differences were observed for the two dietary conditions. DRG from mice on the low-P/s diet had an increase in the rate of fall of both phases of repolarization which, in conjunction with the reduced action potential overshoot, led to a reduced action potential duration. This shift to shorter-duration action potentials was accompanied by a shift to more monophasic falling phases. The low-P/S neurons also exhibited a decreased afterhyperpolarization, decreased specific membrane resistance, and decreased membrane electrical time constant compared to high-P/S neurons. 4. It was concluded that the P/S ratio in the diet can have a significant effect on the electric properties of neurons. The high-P/S neurons tended to have action potentials with biphasic repolarizations and longer durations. In contrast, the low-P/S neurons tended to have action potentials with monophasic repolarizations and shorter durations. Moreover, the known ionic dependence of these two types of action potentials suggested that the low-P/S diet resulted in action potentials with a more exclusive Na dependence, while the high-P/S diet resulted in action potentials with both Na and Ca dependence.     

Mutation induction in Escherichia coli incubated in the reaction mixture of NADPH-dependent lipid peroxidation of rat-liver microsomes

Experiments were carried out to examine mutation induction in E. coli cells incubated in the reaction mixture of NADPH-dependent lipid peroxidation of microsomes isolated from rat liver. The results obtained were as follows: (1) Lipid peroxidation of microsomes occurred extensively on incubation with NADPH and Fe2+. In the E. coli WP2uvrA(pKM101) system, the mutation frequency to streptomycin resistance increased markedly when the cells were incubated in the reaction mixture of microsomal lipid peroxidation. The induced mutation frequencies were dependent on the extent of the lipid peroxidation. (2) It was also found that the mutations were induced at the same rate as in the case of (1) when the cells were added to the microsomal suspensions after the reactions due to the short-lived free radicals had terminated. (3) The cytotoxicity of the lipid peroxidation products was larger in the DNA repair-defective mutant, E. coli SR18 (uvrArecA) than the wild-type strain, SR749. From these results it is concluded that some DNA-damaging and mutagenic substances are indeed produced in the degradation process of peroxidized polyunsaturated fatty acids in liver microsomal lipids.     

The effects of bisulfite on growth and macromolecular synthesis in Escherichia coli

Bisulfite reversibly inhibits the growth of a variety of microorganisms and has been used as a preservative in foods and beverages for that reason. We have now measured macromolecule synthesis in Escherichia coli K12 after bisulfite treatment. RNA synthesis, the synthesis of total protein, and of an inducible enzyme, beta-galactosidase, stopped almost immediately upon addition of 2 mM (or higher concentrations) of bisulfite. These functions resumed after a lag whose duration depended on the concentration of bisulfite added. The synthesis of DNA was slowed upon bisulfite addition, but did not stop entirely. The inhibition of RNA synthesis by bisulfite took place in both stringent and relaxed strains of E. coli and was not relieved upon addition of chloramphenicol. Stringent control was therefore not involved in this effect. No effect on protein synthesis was observed in the cell-free system of E. coli (using poly(U) or MS2 RNA as messenger) at bisulfite concentrations up to 10 mM. Protein synthesis inhibition in vivo was apparently not due to a reaction of bisulfite with a component of this system. In additional experiments, RNA polymerase was not impaired by bisulfite, and the growth inhibition effect was shown to proceed in the presence of inhibitors of free radical chain reactions.     

Retention of human skin fibroblast fatty acid modifications during maintenance culture

Summary The fatty acid composition of cultured human skin fibroblasts was modified by adding either oleic or linoleic acid to the growth medium. After the cultures became confluent, they were washed and transferred to different maintenance media in order to determine the stability of the various fatty acyl modifications. Some changes in fatty acid composition occurred under all conditions. When the maintenance medium was supplemented with fatty acid, the cellular neutral lipid and phospholipid fatty acyl composition were altered markedly within 16 to 24 hr. If no supplemental fatty acid was available during the maintenance period, however, the modified fatty acyl compositions were sufficiently retained so that appreciable differences between the cells enriched with oleate and linoleate persisted for at least 48 to 72 hr. This considerable degree of stability occurred when either 10% delipidized fetal bovine serum or 10% fetal bovine serum containing its inherent lipids were present in the maintenance medium. Although the triglyceride content of the fatty acid-modified cells was quite labile, neither the cholesterol nor phospholipid content changed appreciably during culture in any of the maintenance media. Since the fatty acid compositional differences persisted during several days of maintenance under certain conditions, these modified cultures appear to be a useful experimental system for assessing the effect of lipid structure on fairly long-term cellular functions. This work was supported by Arteriosclerosis Specialized Center of Research Grant HL14230 from the National Heart, Lung and Blood Institute, National Institutes of Health.     

多不饱和脂肪酸合成途径研究进展

多不饱和脂肪酸在大多数生物体膜生物学和信号传递过程中起着至关重要的作用。最近研究发现,一些深海生物合成多不饱和脂肪酸并非由饱和脂肪酸的延长及脱饱和反应,而是由聚酮合酶途径(polyketide synthase,PKS)直接合成。介绍多不饱和脂肪酸的生物合成并总结近年来聚酮合酶这一新途径及其分子机制的研究进展。     

中华稻蝗脂肪提取方法

以丙酮和石油醚的混合液为提取液,通过正交试验,对中华稻蝗Oxyachinensis(Thunberg)成虫体脂肪进行溶剂提取条件的优化研究,并分别讨论了各因素对中华稻蝗成虫体脂肪提取率的影响。结果表明:料液比4/25、溶剂混比1/1(丙酮:石油醚)、提取时间8h、水浴温度85℃为中华稻蝗脂肪提取的最佳工艺条件,在此条件下,脂肪得率可达5.875%。     

ANTARCTIC DISTRIBUTION,PIGMENT AND LIPID COMPOSITION,AND MOLECULAR IDENTIFICATION OF THE BRINE DINOFLAGELLATE POLARELLA GLACIALIS (DINOPHYCEAE)1

Polarella glacialis (Montresor et al.) was identified in Davis Station sea ice by morphological and DNA sequence comparison of cultures with those of the authentic strain P. glacialis CCMP 1383 isolated from McMurdo Sound. Cells and cysts of the Davis isolate (FL1B) were morphologically indistinguishable from P. glacialis, and comparison of the large subunit rDNA of both cultures demonstrated only 0.2% sequence divergence over 1366 base pairs. The photosynthetic pigments of P. glacialis (strains FL1B and CCMP 1383) were typical of dinoflagellates, with peridinin (contributing up to 31%) as the major accessory pigment. Extremely high levels of polyunsaturated fatty acids (PUFA, up to 76.3%) were characteristic of P. glacialis isolate FL1B. The high PUFA concentration of this species is thought to be an adaptation to survive the cold temperatures of the upper fast ice. The sterol profile of FL1B was atypical of dinoflagellates, with 4‐desmethylsterols (up to 79%) in greater abundance than 4α‐methyl sterols (up to 24%). 27‐Nor‐24‐methylcholest‐5,22E‐dien‐3β‐ol was identified as the principle sterol in P. glacialis, contributing up to 64% of the total sterol composition.     

Eicosapentaenoic acid inhibits TNF-alpha-induced matrix metalloproteinase-9 expression in human keratinocytes, HaCaT cells

Eicosapentaenoic acid (EPA) is an omega-3 (ω-3) polyunsaturated fatty acid (PUFA), which has anti-inflammatory and anti-cancer properties. Some reports have demonstrated that EPA inhibits NF-κB activation induced by tumor necrosis factor (TNF)-α or lipopolysaccharide (LPS) in various cells. However, its detailed mode of action is unclear. In this report, we investigated whether EPA inhibits the expression of TNF-α-induced matrix metalloproteinases (MMP)-9 in human immortalized keratinocytes (HaCaT). TNF-α induced MMP-9 expression by NF-κB-dependent pathway. Pretreatment of EPA inhibited TNF-α-induced MMP-9 expression and p65 phosphorylation. However, EPA could not affect IκB-α phosphorylation, nuclear translocation of p65, and DNA binding activity of NF-κB. EPA inhibited TNF-α-induced p65 phosphorylation through p38 and Akt inhibition and this inhibition was IKKα-dependent event. Taken together, we demonstrate that EPA inhibits TNF-α-induced MMP-9 expression through inhibition of p38 and Akt activation.