High‐level exogenous trans10, cis12 conjugated linoleic acid plays an anti‐lipogenesis role in bovine mammary epithelial cells

Primary bovine mammary epithelial cells (BMECs) were treated by 0, 37.5, 75, 112.5, 150 μmol/L trans10, cis12 conjugated linoleic acid (CLA) to evaluate the effects of different level trans10, cis12 CLA on lipogenesis in BMEC. Addition of 75–150 μmol/L trans10, cis12 CLA reduced significantly the triacylglycerol (TAG) content (P < 0.05), but did not have inhibiting action on cell proliferation (P > 0.05). Treatment with 150 μmol/L trans10, cis12 CLA for 48 h resulted in a 17.1% reduction (P < 0.0001) of medium chain fatty acids (MCFA, C14 < C < C16), a 26.5% reduction (P < 0.0001) of unsaturated fatty acids (UFA) and a corresponding reduction of the mRNA abundance of acetyl coenzyme A (acetylCoA) carboxylase (ACC) (P = 0.046), fatty acid synthase (FAS) (P = 0.017) and stearoylCoA desaturase1 (SCD1) (P = 0.002). Another finding was that trans10, cis12 CLA elevated expression of diacylglycerol acyltransferase2 (DGAT2) (P = 0.020) and long chain acylCoA synthetases (ACSL) (P = 0.032). In conclusion, higher trans10, cis12 CLA, not low trans10, cis12 CLA, inhibited milk fat synthesis and changed fatty acid composition by regulating the expression of FAS, ACC, SCD1, DGAT2 and ACSL.     

Purification and characterization of hepatic triacylglycerol lipase isolated from rainbow trout,Oncorhynchus mykiss

Trialcylglycerol (TG) lipase was isolated and partially purified from rainbow trout liver. Triacylglycerol lipase activity was assayed by measuring¹⁴C-oleic acid release from¹⁴C-triolein.¹⁴C-oleic acid release was linear for up to two hours. Optimal activity occurred at pH 7.0 and 15°C. Most of the lipase activity was recovered in the cytosolic fraction. A 27,000-fold purification was achieved after Sepharose (Bio-gel A 0.5 M, 200–400 mesh) chromatography of a resuspended 20% ammonium sulfate fraction. The molecular weight of the trout hepatic lipase as determined by size-exclusion chromatography and by SDS-polyacrylamide gel electrophoresis was 40–43 kD. Lipase-mediated hydrolysis of TG resulted in the production of diacylglycerols, monoacylglycerols, and fatty acids. Kinetic analysis indicated that V_max=0.016 nmol/h/mg protein and that K_m=0.28 mM triolein. Lipolytic activity was enhanced in the presence of cAMP/ATP-Mg²⁺. These results suggest that the liver of trout possesses a neutral TG lipase that is responsible for mobilizing stored TG and is catalytically activated by phosphorylation.A part of this work was presented at the Annual Meeting of the American Society of Zoologists, December 26–30, 1990, San Antonio, TX.     

缺刻缘绿藻二酰甘油酰基转移酶2(DGAT2)的基因特性与功能鉴定

酰基-CoA:二酰甘油酰基转移酶(DGAT)是三酰甘油(TAG)合成过程中的关键酶。在缺刻缘绿藻转录组测序数据库中,通过同源搜索,发现了1个编码DGAT2的cDNA全长序列。该序列长1997 bp,其中,5’-非转录区(UTR)长44 bp,3’-UTR长897 bp,开放阅读框(ORF)长1056 bp,编码一个351个氨基酸的蛋白质,预测的分子量为39.43 kD,等电点为9.46。基于缺刻缘绿藻和其他物种相应的DGAT基因编码蛋白序列所构建的Neighbor-joining(NJ)系统进化树,结果表明该基因与DGAT2聚成一支,显著不同与DGAT1和DGAT3。氨基酸序列比对发现,该基因含有DGAT2所具有的HPHG这4个氨基酸所组成的高度保守特征序列。因此,将该基因命名为MiDGAT2基因。将它的cDNA与其DNA序列进行比较后发现,MiDGAT2基因含有6个内含子,其剪切位点均符合“GT-AG”规则。为进一步了解其功能,利用反转录PCR克隆了该基因的ORF序列,然后将其亚克隆到表达载体pYES2中,成功地构建了重组表达质粒pY-MiDGAT2。通过电穿孔法将该重组质粒转入酿酒酵母TAG合成缺陷株H1246中,经筛选与序列验证得到含有重组质粒pY-MiDGAT2的酵母转化株。酵母转化株在用SC培养基并加入半乳糖诱导表达培养后,其脂类的薄层色谱分析结果表明,所转的MiDGAT2基因能使酵母转化株恢复TAG合成的能力,从而证实了MiDGAT2基因具有DGAT的功能;利用荧光染料Bodipy对酵母细胞的染色结果显示,MiDGAT2基因能使酵母转化株的细胞重现油滴,尽管重建的油滴大小明显比野生型酵母的小。这些研究为缺刻缘绿藻TAG合成代谢途径与调控机理的探讨奠定了基础。     

甘蓝型油菜皖油12种子中含芥酸甘油三酯的空间分布

油菜是重要工业原料芥酸(C22:1)的来源作物,从空间分布的角度解析油菜种子中芥酸积累的机制,为高芥酸油菜育种提供新方法。利用基质辅助激光解吸电离-质谱成像技术,以芥酸含量为26%的甘蓝型油菜皖油12为材料,分析甘油三酯(triacylglycerol, TAG)在种子的外子叶、内子叶及胚轴中的空间分布。结果表明C58、C60和C62类型的TAG主要富集在种子的子叶(包括外子叶和内子叶),而C原子数小于58的TAG则主要富集在胚轴中(除TAG-54:2、TAG-54:3和TAG-56:2~TAG-56:5无分布差异)。分析开花后38 d种子外子叶、内子叶及胚轴中基因FAE1(fatty acid elongase 1)的表达量,发现FAE1在外子叶和内子叶中的表达量分别是胚轴中的约10倍和20倍。结果表明,种子不同部位FAE1表达量的差异是影响含芥酸TAG在种子中分布的主要因素。     

Fatty Acid Production and Direct Acyl Transfer through Polar Lipids Control TAG Biosynthesis during Nitrogen Deprivation in the Halotolerant Alga Dunaliella tertiolecta

The aims of this work were to evaluate the contribution of the free fatty acid (FA) pool to triacylglyceride (TAG) biosynthesis and to try to characterize the mechanism by which FA are assimilated into TAG in the green alga Dunaliella tertiolecta. A time-resolved lipidomic analysis showed that nitrogen (N) deprivation induces a redistribution of total lipidome, particularly of free FA and major polar lipid (PL), in parallel to enhanced accumulation of polyunsaturated TAG. The steady-state concentration of the FA pool, measured by prolonged ¹⁴C-bicarbonate pre-labeling, showed that N deprivation induced a 50% decrease in total FA level within the first 24 h and up to 85% after 96 h. The abundance of oleic acid increased from 50 to 70% of total free FA while polyunsaturated FA (PUFA) disappeared under N deprivation. The FA flux, measured by the rate of incorporation of ¹⁴C-palmitic acid (PlA), suggests partial suppression of phosphatidylcholine (PC) acyl editing and an enhanced turnover of the FA pool and of total digalactosyl-diacylglycerol (DGDG) during N deprivation. Taken together, these results imply that FA biosynthesis is a major rate-controlling stage in TAG biosynthesis in D. tertiolecta and that acyl transfer through PL such as PC and DGDG is the major FA assimilation pathway into TAG in that alga and possibly in other green microalgae. Increasing the availability of FA could lead to enhanced TAG biosynthesis and to improved production of high-value products from microalgae.     

Replacement of a large portion of fish oil by vegetable oils does not affect lipogenesis, lipid transport and tissue lipid uptake in European seabass (Dicentrarchus labrax L.)

In order to investigate the impact of dietary lipid sources on mechanisms involved in lipid deposition, three groups of European seabass fingerlings with average initial body weight of 5.2 ± 1.0 g were fed three diets differing only by lipid source. These diets were: 100% anchovy oil (diet A), 40% anchovy oil-60% mix of vegetable oils (35% linseed, 15% palm, 10% rapeseed) (diet B) and 40% anchovy oil-60% mix of vegetable oils (24% linseed, 12% palm, 24% rapeseed) (diet C). After 64 weeks of rearing, when seabass reached the size of 160 g, the activity of lipogenic enzymes (fatty acid synthetase, glucose-6-phosphate dehydrogenase and malic enzyme) in liver and of lipoprotein lipase (LPL) in perivisceral adipose tissue, liver and white muscle were measured. Transport of lipid by lipoproteins was examined by determining plasma lipid composition and lipoprotein classes. Dietary oil source did not modify growth performance or lipid content of flesh and liver of seabass. Replacement of 60% of fish oil by the two mixtures of vegetable oils had no significant effect on hepatic lipogenesis and activity of LPL in liver and adipose tissue. Activity of LPL in white muscle was decreased in fish fed diet C compared to those fed diets A and B. Diets containing the mixture of vegetable oils led to lowered plasma, VLDL and LDL cholesterol levels compared to diet A.It is concluded that replacing 60% of fish oil by the two mixtures of vegetable oils in the feeds of European seabass fingerlings until they reach the size of 160 g has no marked effect on growth performance, lipogenesis and tissue lipid uptake but has a hypocholesterolemic effect.     

大豆油脂的合成途径及关键酶 GPAT 基因的研究进展

大豆油脂的主要成分为三酰甘油,其合成过程中的关键合成酶基因是甘油三磷酸酰基转移酶(GPAT)基因。如今国内大豆油脂的需求量日渐提高,如何增加大豆油脂的产量将成为油料作物育种的重要目标之一。对大豆油脂、油脂合成途径以及GPAT基因进行了阐述,并介绍了GPAT基因在油脂合成途径中的应用,为进一步筛选可稳定遗传且高效表达的转基因高油脂大豆优良品系奠定基础,对大豆油脂的生产具有重要意义。     

α-亚麻酸对产蛋鸡胆固醇、甘油三酯含量和脂肪酸组成的影响

采用单因素试验设计,研究了日粮中,添加α-亚麻酸00、.5%、1.0%、2.0%、3.0%和4.0%对海兰褐产蛋鸡饲喂4周后蛋黄、卵泡和肝脏中甘油三酯(TG)和总胆固醇(TC)以及蛋黄脂肪酸(FA)的影响。结果表明:蛋黄中亚油酸、亚麻酸、EPA和DHA的含量与日粮中α-亚麻酸添加量呈显著直线或二次曲线增加(P<0.10);蛋黄、各种卵泡中TC均与日粮中α-亚麻酸添加量显著直线或二次曲线降低(P<0.10);蛋黄、卵泡和肝脏的TG以及肝脏的TC与ALA之间的线性和二次曲线降低均不显著(P>0.10)。可见日粮中添加α-亚麻酸能降低胆固醇,提高鸡蛋中PUFA的含量。     

Spatial distribution of functional components in the starchy endosperm of wheat grains

The starchy endosperm of the mature wheat grain comprises three major cell types, namely sub-aleurone cells, prismatic cells and central cells, which differ in their contents of functional components: gluten proteins, starch, cell wall polysaccharides (dietary fibre) and lipids. Gradients are established during grain development but may be modified during grain maturation and are affected by plant nutrition, particularly nitrogen application, and environmental factors. Although the molecular controls of their formation are unknown, the high content of protein and low content of starch of sub-aleurone cells, compared to the other starchy endosperm cells types, may result from differences in developmental programming related to the cells having a separate origin (from anticlinal division of the aleurone cells). The gradients within the grain may be reflected in differences in the compositions of mill streams, particularly those streams enriched in the central and outer cells of the starchy endosperm, respectively, allowing the production of specialist flours for specific end uses.     

高油酸花生油低温分层现象分析

高油酸花生油以其营养价值高、储藏期长等优点越来越受到广大消费者的青睐。在低温条件(4~6℃)下,普通花生油会发生凝固现象,而高油酸花生油则不会完全凝固,而是产生分层现象。为了探究高油酸花生油低温下分层的原因,对分层后的高油酸花生油上、下层的脂肪酸及甘油三酯组成进行了分析,发现下层油中饱和脂肪酸(SFA)含量显著增加,特别是超长链饱和脂肪酸(VLCSFA)的含量是上层油的3.8倍。甘油三酯分析表明,下层油中携带2个SFA的甘油三酯(S2U)显著富集,特别是携带VLCSFA的S2U型甘油三酯,其在下层油中的含量是上层油中含量的7.1倍。由此推断,大量携带VLCSFA的S2U型甘油三酯在低温下结晶析出是导致高油酸花生油分层的主要原因。