菜豆叶片衰老期间叶绿体被膜膜脂与脂肪酸组分的变化

菜豆叶片叶绿体总脂和被膜膜脂中均含有单半乳糖甘油二脂和双半乳糖甘油二脂,在整个衰老期间两种糖脂的比值变化不大。叶绿体总脂中含有5种磷脂,脂肪酸以不饱和的亚麻酸为主,而被膜膜脂中仅含磷脂酰胆碱和磷脂酰甘油,脂肪酸以饱和的棕榈酸为主,不饱和亚油酸为次。叶片衰老过程中被膜所含两种磷脂比值明显降低,脂肪酸的不饱和指数也因亚麻酸相对含量显著减少、棕榈酸相对含量增加而降低。     

集胞藻Synechocystis sp. PCC 6803脂质组的分析

以集胞藻Synechocystis sp. PCC 6803为研究对象, 研究建立了基于超高效液相色谱耦合串联质谱技术脂质组学分析方法。鸟枪法脂质组学通过电喷雾离子化有效分离油脂粗提物中所含单个脂质分子, 在三重四极杆扫描碎片离子, 能够利用特征片段离子鉴定光合甘油酯的种类和酰基组成, 具有高效、灵敏度高和质量准确度高等优点。对不同光强下生长的Synechocystis sp. PCC 6803细胞的各脂质组分进行了全定量分析, 发现单半乳糖甘油二酯 (Monogalactosyldiacylglycerol, MGDG)和磷脂酰甘油(Phosphatidyl glycerol, PG)在高光处理的第2小时即显著积累, 增长量分别为34.64%和68.49%, 其中以含有从头合成、高度饱和的脂肪酸的种类增长最为快速和显著, 而后高不饱和度的脂肪酸组成的种类逐渐积累。双半乳糖甘油二脂(Digalactosyldiacylglycerol, DGDG)在各时间点都持续增长, 12h后增长量达26.95%, 硫代异鼠李糖甘油二酯(Sulfoquinovosyl diacylglycerol, SQDG)的含量则呈现出不断下降的趋势。研究所建立的脂质组学分析方法对进一步研究Synechocystis sp. PCC 6803的脂质代谢及生理功能提供了有力的分析工具。     

儿茶素诱导的拟南芥根细胞膜脂变化

儿茶素是一种可以短时间内杀死植物细胞的植物毒素,由于具有强的植物毒性,儿茶素是开发除草剂的理想化合物,它可以诱导植物根系统的死亡.为了研究植物根细胞膜脂对化学胁迫的响应规律,我们运用高通量的脂类组学方法检测了拟南芥根中膜脂分子的组成,比较了儿茶素处理下拟南芥野生型(WS)及磷脂酶Dδ缺失突变体( PLDδ-KO)根中膜脂分子的组成情况、膜脂含量、双键指数及碳链长度值.结果发现,儿茶素处理拟南芥根90 min后,二半乳糖基二酰甘油(DGDG)、单半乳糖基二酰甘油(MGDG)、磷脂酰甘油(PG)、磷脂酰胆碱(PC)及磷脂酰肌醇(PI)的总含量在WS与PLDδ-KO植株根中都显著下降,磷脂酰乙醇胺(PE)和磷脂酰丝氨酸(PS)在WS中下降,在PLDδ-KO中上升.儿茶素处理导致PLDδ-KO植株的PC/PE比值显著下降,WS植株PS碳链长度显著增加.上述结果说明儿茶素处理后,磷脂酶Dδ缺失突变体膜不稳定性增加,PLDδ-KO植株对儿茶素胁迫更加敏感.     

海滨盐薄片菌——分离自海洋盐田的一个嗜盐古菌新种（英文）

【目的】研究分离自我国华南地区阳江盐田的一株嗜盐古菌菌株YJ-41~T,探究其分类学地位。【方法】运用多相分类学方法即通过表型和遗传型特征鉴定,研究菌株YJ-41T的分类学地位。【结果】菌株YJ-41~T的细胞为杆状、革兰氏染色阴性、菌落呈红色。菌株YJ-41T的生长温度范围20–50°C(最适为37°C)、Na Cl浓度范围2.1–4.8 mol/L(最适为3.1 mol/L)、MgCl_2浓度范围0–1.0 mol/L(最适为0.05 mol/L)、pH范围5.0–9.0(最适为pH 7.0)。细胞在蒸馏水中会裂解,维持细胞形态的最低Na Cl浓度为10%(质量体积比)。菌株YJ-41~T的极性脂为磷脂酸(Phosphatidic acid,PA)、磷脂酰甘油(Phosphatidyl glycerol,PG)、磷脂酰甘油磷酸甲基酯(Phosphatidyl glycerol phosphate methyl ester,PGP-Me)、磷脂酰甘油硫酸酯(Phosphatidyl glycerol sulphate,PGS)和8种糖脂;其中3种糖脂为硫酸甘露糖苷葡萄糖二醚(Sulfated mannosyl glucosyl diether,S-DGD-1)、半乳糖苷甘露糖苷葡萄糖二醚(Galactosyl mannosy glucosyl diether,TGD-1)和甘露糖苷葡萄糖二醚(Mannosyl glucosyl diether,DGD-1),其余为未知糖脂。菌株YJ-41~T的16S rRNA基因和rpo B′基因与盐薄片菌属(Halolamina)的成员相关基因相似性分别为97.5%–98.4%和93.1%–94.4%。菌株YJ-41T的G+C mol%为61.4 mol%。【结论】表型、化学分类和系统发育的特性表明,菌株YJ-41T(=CGMCC 1.12859T=JCM 30237T)代表Halolamina属的一个新种,建议命名为海滨盐薄片菌(Halolamina litorea)。     

甘油-3-磷酸酰基转移酶在植物脂质代谢、生长及逆境反应中的作用

甘油脂质是高等植物中含量最丰富的脂质,其种类包括磷脂、糖脂、油脂及胞外脂质等,广泛参与不同的生物过程。甘油-3-磷酸酰基转移酶(GPAT)利用各种脂肪族酰基或其衍生物作为底物催化甘油-3-磷酸(G3P)脂酰基化反应形成溶血磷脂酸(LPA),是脂质合成代谢途径中的限速酶。植物GPAT家族含有多个成员,根据其亚细胞定位、酶活性及底物选择性,拟南芥GPAT家族10个成员可分为3类。不同的GPAT具有独特的分子结构、活性调控及时空分布,并参与膜磷脂、甘油三脂、角质及软木脂合成代谢过程。研究表明极具分子异质性的GPAT在植物生长、发育和逆境胁迫反应过程中发挥着重要作用。     

三角褐指藻甘油酯对氮胁迫的响应

【背景】三角褐指藻作为生物燃料潜在的生产者,在胁迫条件下能通过改变其甘油酯组成来适应外部环境的变化,同时伴随着生物燃料原料甘油三酯(TAG)的积累,研究三角褐指藻甘油酯对氮胁迫的响应机制有利于深入认识TAG的积累过程。【目的】通过分析三角褐指藻在正常和氮胁迫条件下各类脂质含量及其脂肪酸成分的变化,揭示氮胁迫诱导积累的TAG酰基主要来源,以及在胁迫前生成的各极性甘油酯脂肪酸的去向,从而为进一步认识三角褐指藻对氮胁迫的响应机制提供新信息。【方法】利用高效薄层色谱结合气相色谱法分析三角褐指藻在正常和氮胁迫条件下的脂肪酸及甘油酯组分的变化。【结果】三角褐指藻在氮胁迫条件下TAG含量增加至57.8 mg/g时,总甘油酯含量几乎不变,但各甘油酯含量变化差异很大,表现为各极性脂含量显著降低。在此期间,各类甘油酯脂肪酸组成含量的变化表明,三角褐指藻TAG主要积累饱和及单不饱和脂肪酸,即16:0和16:1n7,分别以从头合成及原有极性脂转化为主,极性脂的部分二十碳五烯酸(EPA)作为酰基供体也向TAG发生了转化;此外组成极性脂的多不饱和脂肪酸16:2n4、16:3n4及EPA分解导致其含量显著下降。【结论】当氮胁迫诱导的三角褐指藻TAG含量为57.8 mg/g时,积累的TAG酰基中有48%来自从头合成,52%来自极性脂转化;而氮胁迫诱导所减少的极性脂酰基中有54%转化成TAG,46%发生了分解。     

微藻三酰甘油合成途径及其最新研究进展

三酰甘油(triacylglycerols,TAGs)是动物、植物、微生物和微藻细胞主要的储藏性脂类,它可应用于食品、轻工业和生物燃料等方面,是一种新型可再生能源——生物柴油生产的重要原料。与高等油料作物相比,微藻具有光合作用效率高、生长速度快、油脂产量高、不占用农业耕地和适应多种生长环境等优势,是一种潜在的新型生物柴油生产原料。然而,目前人们对有机体,尤其是微藻细胞内TAG合成与积累的分子机制及细胞的代谢调控机制还知之甚少。对TAG合成的一系列重要过程,包括脂肪酸的合成,TAG生物合成的主要途径和旁路途径,以及与TAG合成相关的关键酶和重要基因等进行了综述,特别对微藻细胞中与TAG合成相关的关键基因的最新研究进展进行了总结,旨在更好地了解油脂代谢的调控途径,为最大限度地供应生物柴油的生产原料提供理论基础。     

ESI-MS MS方法检测拟南芥膜脂分子对机械伤害的响应

利用一种灵敏的、基于ESI-MS􊄯MS ( electrospray ionization tandem mass spectrometry) 的脂类组学方法,测定了机械伤害诱导的拟南芥6 种磷 (phospholipids) 、2 种糖脂(glycolipids) 、3 种溶血磷脂( lysophospholipids)和约120 种脂类分子的变化, 探索了膜脂响应机械伤害的基本趋势。结果表明, 机械伤害后磷脂酸( phosphatidic acid , PA) 和3 种溶血磷脂显著升高, 而叶绿体膜上的糖脂减少; 在测量的1 小时范围内, 不同脂类水解产生的磷脂酸分子的增加速度和强度不同, 反映出它们经历了不同的生化过程。具体表现为:(1 ) 叶绿体膜脂磷脂酰甘油(phosphatidylglycero , PG) 分子34∶4 PG 水解的产物磷脂酸分子34∶4 PA 的积累速度明显慢于其它磷脂酸分子; (2) 磷脂酸分子34∶6 PA 仅有少量的积累, 其可能是由叶绿体膜脂单半乳糖二酰甘油(monogalactosyldiacylglycerol, MGDG) 。分子34∶6 MGDG 和双半乳糖二酰甘油( digalactosyldiacylglycerol, DGDG) 分子34∶6 DGDG 水解产生, 然而这两种糖脂含量明显下降, 说明它们有可能还参与了其它的反应。脂类的摩尔百分组成没有剧烈的变化。     

儿茶素诱导的拟南芥根细胞膜脂变化

儿茶素是一种可以短时间内杀死植物细胞的植物毒素,由于具有强的植物毒性,儿茶素是开发除草剂的理想化合物,它可以诱导植物根系统的死亡。为了研究植物根细胞膜脂对化学胁迫的响应规律,我们运用高通量的脂类组学方法检测了拟南芥根中膜脂分子的组成,比较了儿茶素处理下拟南芥野生型（WS）及磷脂酶Dδ缺失突变体（PLDδ KO）根中膜脂分子的组成情况、膜脂含量、双键指数及碳链长度值。结果发现,儿茶素处理拟南芥根90min后,二半乳糖基二酰甘油（DGDG）、单半乳糖基二酰甘油（MGDG）、磷脂酰甘油（PG）、磷脂酰胆碱（PC）及磷脂酰肌醇（PI）的总含量在WS与PLDδ KO植株根中都显著下降,磷脂酰乙醇胺（PE）和磷脂酰丝氨酸（PS）在WS中下降,在PLDδ KO中上升。儿茶素处理导致PLDδ KO植株的PC/PE比值显著下降,WS植株PS碳链长度显著增加。上述结果说明儿茶素处理后,磷脂酶Dδ缺失突变体膜不稳定性增加,PLDδ KO植株对儿茶素胁迫更加敏感。     

HPLC-ELSD快速测定微藻中性脂

溶剂法提取微藻油脂不同于植物种子油脂,它是全细胞的提取物,成分非常复杂,存在与甘油三酯(TAG)在色谱保留性质上相近的低极性物质,干扰TAG的测定。建立了基于二醇基柱及蒸发光检测器、正己烷-异丙醇为流动相的快速测定微藻中性脂的方法。对该方法进行评价,结果显示,测定的TAG、游离脂肪酸(FFA)、甘油二酯(DAG)、甘油一酯(MAG)线性相关系数均大于0.99,方法重复性好。湛江等鞭金藻及微拟球藻样品中TAG加标回收率为96.2%~113.1%,相对标准偏差(RSD)为0.46%~4.8%。将本方法测定湛江等鞭金藻及微拟球藻中TAG的含量并与传统的固相萃取(SPE)及常用的TLC/GC测定TAG的方法进行比较,相比上述两种方法,该方法前处理简单、灵敏度高,可快速准确测定微藻中TAG的含量。     

Remodelling of triacylglycerols in microsomal preparations from developing castor bean (Ricinus communis L.) endosperm

Microsomal preparations from developing castor bean (Ricinus communis L.) endosperm catalyzed remodelling of in-situ-formed triacylglycerol (TAG) species. Castor bean microsomal membranes synthesized [¹⁴C]TAGs from either glycerol 3-phosphate and [¹⁴C]ricinoleoyl-CoA or [¹⁴C]glycerol 3-phosphate and ricinoleoyl-CoA. Upon repelleting and subsequent incubation of the microsomes a redistribution occurred of both the [¹⁴C]glycerol and [¹⁴C]ricinoleoyl moieties of the in-situ-synthesized [¹⁴C]TAGs. Radioactivity was transferred from TAG species with three (3HO-TAG) or two (2HO-TAG)ricinoleoyl groups into species with two or one (HO-TAG) ricinoleoyl groups. Mass analysis of the lipid and fatty acid movements in the membranes showed that a net synthesis of TAGs with no, one and two ricinoleoyl groups occurred at the expense of 3HO-TAG and polar lipids. Thus, the non-hydroxylated acyl groups from polar lipids were used in the remodelling of TAGs. In-vivo feeding of [¹⁴C]ricinoleic acid to slices of castor bean endosperm demonstrated the presence of two radioactive pools of TAGs one in the oil bodies, which was rich in [¹⁴C]3HO-TAG, and one associated with the microsomal membranes, which was dominated by radioactive 1HO-TAG and 2HO-TAG. The microsomal TAG pool was remodelled in vivo in a similar way as in the in-vitro experiments with microsomal membranes. Received: 8 November 1996 / Accepted: 5 February 1997     

Apparent Role of Phosphatidylcholine in the Metabolism of Petroselinic Acid in Developing Umbelliferae Endosperm

Studies were conducted to characterize the metabolism of the unusual fatty acid petroselinic acid (18:1cis[delta]6) in developing endosperm of the Umbelliferae species coriander (Coriandrum sativum L.) and carrot (Daucus carota L.). Analyses of fatty acid compositions of glycerolipids of these tissues revealed a dissimilar distribution of petroselinic acid in triacylglycerols (TAG) and the major polar lipids phosphatidylcholine (PC) and phosphatidylethanolamine (PE). Petroselinic acid comprised 70 to 75 mol% of the fatty acids of TAG but only 9 to 20 mol% of the fatty acids of PC and PE. Although such data appeared to suggest that petroselinic acid is at least partially excluded from polar lipids, results of [1-14C]acetate radiolabeling experiments gave a much different picture of the metabolism of this fatty acid. In time-course labeling of carrot endosperm, [1-14C]acetate was rapidly incorporated into PC in high levels. Through 30 min, radiolabel was most concentrated in PC, and of this, 80 to 85% was in the form of petroselinic acid. One explanation for the large disparity in amounts of petroselinic acid in PC as determined by fatty acid mass analyses and 14C radiolabeling is that turnover of these lipids or the fatty acids of these lipids results in relatively low accumulation of petroselinic acid mass. Consistent with this, the kinetics of [1-14C]acetate time-course labeling of carrot endosperm and "pulse-chase" labeling of coriander endosperm suggested a possible flux of fatty acids from PC into TAG. In time-course experiments, radiolabel initially entered PC at the highest rates but accumulated in TAG at later time points. Similarly, in pulse-chase studies, losses in absolute amounts of radioactivity from PC were accompanied by significant increases of radiolabel in TAG. In addition, stereospecific analyses of unlabeled and [1-14C]acetate-labeled PC of coriander endosperm indicated that petroselinic acid can be readily incorporated into both the sn-1 and sn-2 positions of this lipid. Because petroselinic acid is neither synthesized nor further modified on polar lipids, the apparent metabolism of this fatty acid through PC (and possibly through other polar lipids) may define a function of PC in TAG assembly apart from its involvement in fatty acid modification reactions.     

ACCLIMATION OF PROROCENTRUM MINIMUM (DINOPHYCEAE) TO PROLONGED DARKNESS BY USE OF AN ALTERNATIVE CARBON SOURCE FROM TRIACYLGLYCERIDES AND GALACTOLIPIDS

The dinoflagellate Prorocentrum minimum (Pavillard) Schiller is known to be a major bloom-causing microalga in the southern ocean of the Korean peninsula. The acclimation of this alga to darkness for 10 days was investigated by analyzing the content of various lipids, such as phospholipid (PL), galactolipid (GL), and triacylglyceride (TAG). Actively growing cultures of the alga under normal growth conditions (14:10 h LD [light:dark] cycle) were transferred to a growth chamber under conditions of no light and no carbon sources in the medium, and the culture was continued for another 10 days. The results showed that the content of TAG and GL decreased gradually during dark incubation, whereas the total PL content changed little; PC, PE, and PG decreased; and PS, PA, and PI increased. An increase in the activity of β-oxidation and isocitrate lyase (ICL, a glyoxylate cycle enzyme) paralleled the decrease of TAG and GL. These observations strongly suggested that TAG and GL were utilized as alternative carbon sources by the cells under the prolonged dark cultivation. Light treatment of the cells cultivated in the dark for 10 days allowed them to attain the lipid composition that was observed in cells grown in light. These results strongly suggested that the cells maintained their metabolic integrity without unrecoverable cellular damages or cell death during 10 days of dark cultivation.     

Metabolic pathways for dietary lipids in the midgut of hematophagous Panstrongylus megistus (Hemiptera: Reduviidae)

The metabolism of dietary lipids in the anterior midgut of Panstrongylus megistus during blood digestion was studied. Fifth instar nymphs were fed a blood meal containing 7.1 +/- 0.4 mg of lipids, consisting mainly of triacylglycerol (TAG), and completed the overall process of digestion in about 20 days. Lipolysis of TAG and pathways for diacylglycerol (DAG) biosynthesis in the midgut were investigated by feeding the insects with [9,10-3H]-oleic acid-labeled triolein. Lumenal [3H]-triacylglycerol was hydrolyzed, generating mainly fatty acids (FA) and glycerol and to lesser extent, DAG. Almost no radioactivity associated with monoacylglycerol was found at any time. In midgut tissue, labeled fatty acids were incorporated into phosphatidic acid, DAG and TAG, whereas no significantly labeled monoacylglycerol was observed. In addition, the activities of enzymes related to DAG metabolism were assayed in non-blood fed midgut homogenates and at different times after feeding on a blood meal. Significant changes in the activities of phosphatidate phosphohydrolase (EC 3.1.3.4) and triacylglycerol lipase (EC 3.1.1.3) were observed during blood digestion, suggesting that these enzymes are important in regulating intracellular DAG synthesis and mobilization in midgut cells. Finally, the histological changes of lipid stores observed in anterior midgut confirmed the active process of uptake and trafficking of lipids performed by the enterocytes during blood digestion.     

Differential distribution and metabolism of arachidonic acid and docosahexaenoic acid by human placental choriocarcinoma (BeWo) cells

The time course of incorporation of [¹⁴C]arachidonic acid and [³H]docosahexaenoic acid into various lipid fractions in placental choriocarcinoma (BeWo) cells was investigated. BeWo cells were found to rapidly incorporate exogenous [¹⁴C]arachidonic acid and [³H] docosahexaenoic acid into the total cellular lipid pool. The extent of docosahexaenoic acid esterification was more rapid than for arachidonic acid, although this difference abated with time to leave only a small percentage of the fatty acids in their unesterified form. Furthermore, uptake was found to be saturable. In the cellular lipids these fatty acids were mainly esterified into the phospholipid (PL) and the triacyglycerol (TAG) fractions. Smaller amounts were also detected in the diacylglycerol and cholesterol ester fractions. Almost 60% of the total amount of [3H]Docosahexaenoic acid taken up by the cells was esterified into TAG whereas 37% was in PL fractions. For arachidonic acid the reverse was true, 60% of the total uptake was incorporated into PL fractions whereas less than 35% was in TAG. Marked differences were also found in the distribution of the fatty acids into individual phospholipid classes. The higher incorporation of docosahexaenoic acid and arachidonic acid was found in PC and PE, respectively. The greater cellular uptake of docosahexaenoic acid and its preferential incorporation in TAG suggests that both uptake and transport modes of this fatty acid by the placenta to fetus is different from that of arachidonic acid.     

High-altitude acclimation increases the triacylglycerol/fatty acid cycle at rest and during exercise

High-altitude acclimation alters lipid metabolism during exercise, but it is unknown whether this involves changes in rates of lipolysis or reesterification, which form the triacylglycerol/fatty acid (TAG/FA) cycle. We combined indirect calorimetry with [2-(3)H]glycerol and [1-(14)C]palmitate infusions to simultaneously measure total lipid oxidation, lipolysis, and rate of appearance (R(a)) of nonesterified fatty acids (NEFA) in high-altitude-acclimated (HA) rats exercising at 60% maximal O(2) uptake (VO(2 max)). During exercise, relative total lipid oxidation (%VO(2)) equaled sea-level control (SL) values; however, acclimation greatly stimulated lipolysis (+75%) but had no effect on R(a) NEFA. As a result, TAG/FA cycling increased (+119%), due solely to an increase in recycling (+144%) within adipocytes. There was no change in either group in these variables with the transition from rest to exercise. We conclude that, in HA, 1) acclimation is a potent stimulator of lipolysis; 2) rats do not modify TAG/FA cycling with the transition to exercise; and 3) in normoxia, HA and SL derive the same fraction of their total energy from lipids and carbohydrates.     

Effects of modulation of glycerol kinase expression on lipid and carbohydrate metabolism in human muscle cells.

Glycerol is taken up by human muscle in vivo and incorporated into lipids, but little is known about regulation of glycerol metabolism in this tissue. In this study, we have analyzed the role of glycerol kinase (GlK) in the regulation of glycerol metabolism in primary cultured human muscle cells. Isolated human muscle cells exhibited lower GlK activity than fresh muscle explants, but the activity in cultured cells was increased by exposure to insulin. [U-(14)C]Glycerol was incorporated into cellular phospholipids and triacylglycerides (TAGs), but little or no increase in TAG content or lactate release was observed in response to changes in the medium glycerol concentration. Adenovirus-mediated delivery of the Escherichia coli GlK gene (AdCMV-GlK) into muscle cells caused a 30-fold increase in GlK activity, which was associated with a marked rise in the labeling of phospholipid or TAG from [U-(14)C]glycerol compared with controls. Moreover, GlK overexpression caused [U-(14)C]glycerol to be incorporated into glycogen, which was dependent on the activation of glycogen synthase. Co-incubation of AdCMV-GlK-treated muscle cells with glycerol and oleate resulted in a large accumulation of TAG and an increase in lactate production. We conclude that GlK is the limiting step in muscle cell glycerol metabolism. Glycerol 3-phosphate is readily used for TAG synthesis but can also be diverted to form glycolytic intermediates that are in turn converted to glycogen or lactate. Given the high levels of glycerol in muscle interstitial fluid, these finding suggest that changes in GlK activity in muscle can exert important influences on fuel deposition in this tissue.     

Ferrylmyoglobin impairs secretion of VLDL triacylglycerols from stored intracellular pools: involvement of lipid peroxidation

Ferrylmyoglobin (ferrylMb) may play a major role in vivo under certain pathological conditions. Preliminary experiments showed that ferrylmyoglobin induced a mild oxidative stress in rat hepatocytes, mainly reflected by early lipid peroxidation. One of the major functions of hepatocytes is the synthesis, secretion and distribution of lipids to other cells. The aim of this work was to examine whether ferrylMb affected the synthesis and secretion of triacylglycerols (TAG), and the possible involvement of lipid peroxidation on these effects. The heme protein completely impaired VLDL secretion, affecting both the lipid and apoB components of the lipoprotein particle. The incorporation of [(3)H]-oleate into newly synthesized diacylglycerol and TAG was not altered by ferrylMb. The co-treatment of cells with alpha-tocopherol prevented lipid peroxidation and concomitantly reverted VLDL TAG secretion to control values. Importantly, although ferrylMb dramatically blocked prelabeled TAG secretion, newly synthesized TAG secretion was not impaired. These data indicate that lipid peroxidation elicited by ferrylMb modulates the VLDL TAG secretion process, specifically affecting the stored intracellular TAG mobilization, rather than de novo synthesis. Apart from its potential role in vivo, ferrylmyoglobin constitutes a useful model for studying the interactions between lipid peroxidation and the specific TAG pool dependence for VLDL secretion.     

Distribution and metabolism of arachidonic and docosahexaenoic acids in rat pineal cells. Effect of norepinephrine

The time-course incorporation of 10 μM [¹⁴C]arachidonic (AA) and docosahexaenoic (DHA) acids into glycerolipids was studied in rat pineal cells. The incorporation of both labeled fatty acids into total lipids was approximately equal, but their distribution profiles among the various cell lipids showed marked differences. The esterification of [¹⁴C]DHA in the neutral lipids, triacylglycerols (TAG) and cholesterol esters (CE), was 2-fold higher than that of [¹⁴C]AA whereas the opposite could be observed in total phospholipids (PL). The order of incorporation into PL was phosphatidylcholine (PC) > phosphatidylinositol (PI) = phosphatidylethanolamine (PE) for [¹⁴C]AA and PC = PE for [¹⁴C]DHA, the incorporation of both fatty acids being not detected in phosphatidylserine (PS) and that of DHA not in PI. When using 0.5 μM [³H] fatty acids, the respective distribution patterns resembled that of fatty acids at 10 μM, except for a lower proportion in TAG. The stimulation of ³H-labeled cells by 100 μM norepinephrine induced a 170% increase of basal release of [³H]AA into the medium, while [³H]DHA was virtually not released. However, the analysis of cell labeling revealed that both [³H] fatty acid levels were decreased in PL and increased in TAG. These findings suggest different involvement for AA and DHA in the pineal function. The preferential incorporation of DHA in TAG suggests that TAG might play an important role in the pineal enrichment with DHA. The absence of DHA release after NE stimulation, which however cannot be ascertained, may raise the question of the role of DHA in NE transduction.