Reconstitution of a phospholipid flippase from rat liver microsomes

The endoplasmic reticulum is the principal site of synthesis and initial incorporation of membrane lipids in eukaryotic cells; the enzymes of glycerolipid biosynthesis are exclusively located on its cytoplasmic surface. To maintain a phospholipid bilayer in this organelle, newly synthesized phospholipids must be translocated to the lumenal surface. Consistent with this are measurements indicating that movement of phospholipids across microsomal membranes is rapid, with a half-time less than 5 min (refs 3 and 4). Rapid movement of phospholipids has also been detected across the plasma membrane of Bacillus megaterium, another site of de novo lipid biosynthesis. The rapid transmembrane movement of phosphatidylcholine has not been detected, however, in vesicles prepared from microsomal lipids. These latter data suggest involvement in the endoplasmic reticulum of a phospholipid-translocating protein, as was first proposed by Bretscher who called it 'flippase'. Here we report reconstitution of a phospholipid flippase from rat liver microsomes into lipid vesicles.     

Metabolism of fibrates by cytochrome P450s and UDP-glycosyltransferases in rat and human liver microsomes

Fibrates are widely used for the treatment of dyslipidemia.However,the contributions of the phase I and phase II metabolic pathways to the clearance of fibrates are unclear.In this study,we investigated the metabolism of gemfibrozil(Gem) ,clofibric acid(CA) ,fenofibric acid(FA) and bezafibrate(Beza) by cytochrome P450s(P450s) and UDP-glycosyltransferases(UGTs) using a substrate depletion approach.We also compared the metabolic characteristics of rat liver microsomes(RLM) and human liver microsomes(HLM) .The intrinsic clearance rates mediated by P450s,UGTs and both were 172 ± 22,643 ± 26,798 ± 103 μL min-1 mg-1,respectively,for Gem and 43 ± 11,88 ± 12,119 ± 15 μL min-1 mg-1,respectively,for CA in RLM.The fractions metabolized by P450s and UGTs in RLM were 22% and 81% for Gem,36% and 74% for CA.The P450-and UGT-mediated depletion rates for Gem were 303 and 1607 nmol min-1 mg-1 in RLM versus 86 and 243 nmol min-1 mg-1 in HLM.The corre-sponding rates for CA were 1.1 and 1.7 nmol min-1 mg-1 in RLM versus 0.025 and 0.038 nmol min-1 mg-1 in HLM.Accordingly,both P450s and UGTs substantially contribute to the clearance of Gem and CA,with UGTs playing a greater role.To avoid un-der-estimating the impact of these pathways,it is necessary to measure NADPH-and UDPGA-dependent metabolism.Although the fractions of these two pathways in RLM and HLM were similar,the depletion rate of Gem and CA in RLM was higher than that in HLM.The metabolism of FA and Beza by P450s and UGTs was too low to calculate intrinsic clearance in both RLM and HLM.These results indicate that fibrates are metabolized via similar pathways in rats and humans,and it is applicable to use RLM to predict the clearance of fibrates in human.     

大黄5种蒽醌类成分在大鼠肝微粒体中的代谢及酶促反应动力学

研究大黄5种蒽醌类成分在大鼠肝微粒体中的代谢特征和参与代谢的细胞色素P450亚型.超速离心法制备大鼠肝微粒体,采用反相高效液相色谱(RP-HPLC)测定孵育液中大黄5种蒽醌类成分的质量浓度,研究大黄蒽醌类成分的酶促动力学,推导药物米氏常数(Km)和最大反应速度(Vmax),并计算体外酶对药物的清除率(Clint);用苯巴比妥钠(PB)、地塞米松(DEX)、β-奈黄酮(β-NF)诱导大鼠肝微粒体,观察大黄5种蒽醌类成分在各温孵体系中的代谢,同时观察不同质量浓度和不同种类的CYP酶特异性抑制剂对大黄蒽醌类成分代谢的影响.结果表明大黄芦荟大黄素、大黄酸、大黄素、大黄酚、大黄素甲醚在肝微粒体中的Km、Vmax、Clint分别为(18.97±1.89)、(2.50±0.11)、(15.68±1.09)、(183.41±1.90)、(1.37±0.14)mg·L-1;(0.52±0.015)、(0.066±0.003)、(0.41±0.009)、(5.22±0.09)、(0.036±0.0034)mg·L-1·min-1;(2.69±0.12)、(2.56±0.16)、(2.61±0.20)、(2.81±0.10)、(2.63±0.18)min-1·10-2;经DEX、PB、β-NF诱导后,PB组、DEX组大黄蒽醌类成分代谢率高于CMC-Na组,具有显著性差异(P0.05),β-NF组大黄蒽醌类成分代谢率低于CMC-Na组,无显著性差异(P0.05);非那西汀、氟康唑、酮康唑的Dixon图均为一组相交于第二象限的直线.通过研究得知大黄5种蒽醌类成分在PB、DEX诱导的肝微粒体中代谢较快,CYP3A4、CYP2A6为介导大黄蒽醌类成分代谢的主要代谢酶;非那西汀、氟康唑、酮康唑均为为大黄蒽醌类成分的竞争性抑制剂.     

Rapid mobilization of Ca2+ from rat insulinoma microsomes by inositol-1,4,5-trisphosphate

Several hormones and neurotransmitters raise the cytosolic free Ca2+ concentration by stimulating the influx of Ca2+ and/or by mobilizing stored Ca2+. However, the link between the agonist receptor on the cell surface and the organelle(s) from which Ca2+ is mobilized is unknown. One feature of the agonists that increase cytosolic Ca2+ is their rapid induction of phosphatidylinositol turnover and polyphosphoinositide hydrolysis; in some tissues this leads, within seconds, to a marked accumulation of the water-soluble products, inositol 1,4-bisphosphate ( Ins1 , 4P2 ) and inositol-1,4,5- trisphosphate ( Ins1 ,4, 5P3 ), suggesting that these might mediate Ca2+ mobilization from internal pools. Such an action of Ins1 ,4, 5P3 has recently been inferred from studies with permeabilized pancreatic acinar cells and hepatocytes. Here we show directly that Ins1 ,4, 5P3 rapidly releases Ca2+ from a microsomal fraction of rat insulinoma but not from mitochondria or secretory granules. Moreover, this response is transient and desensitizes the microsomes to subsequent Ins1 ,4, 5P3 additions. These results suggest that Ins1 ,4, 5P3 functions as a cellular messenger inducing early mobilization of Ca2+ from the endoplasmic reticulum.     

紫红链霉菌、自养黄色杆菌对钉螺肝细胞损伤的亚显微观察

用透射电镜观察了钉螺经紫色链霉菌(28菌株)和自养黄色杆菌(129菌株)处理后肝细胞结构的变化．结果显示，两种菌处理24h后细胞核核仁消失，核质稀疏，内质网略有损伤，其它变化不明显；48h后，内质网开始分解，尤以紫红链霉菌28处理更为严重，内质网几乎完全分解，并有大量线粒体和溶酶体出现．中也探讨了钉螺可能的致死原因，为探明紫红链霉菌和自养黄色杆菌的灭螺机理提供了依据．     

氯化汞染毒小鼠肝脏及卵巢中LDH和EST同工酶酶谱分析

利用聚丙烯酰胺胶电泳，对氯化汞染毒小鼠的肝脏和卵巢中乳酸脱氢酶（LDH）同工酶和酯酶（EST）同工酶进行了分析。酶谱比较的结果表明，各实验组LDH及EST表达模式与水平同对照组比较均表现出一定的差异，其差异程度呈剂量反应关系。     

酶标法测定脑脊液和血清中的苯巴比妥钠

目的:建立一种适用于实验室高通量测定动物脑脊液和血清中苯巴比妥纳药物浓度的方法.方法:通过测定各反应物的吸收光谱,确定荷移反应络合物的波长,并使用该波长分别测定苯巴比妥钠在去离子水、动物脑脊液和动物血清中的吸光度,并制定标准曲线.同时通过重复测定特定浓度的苯巴比妥钠吸光度进行仪器稳定性分析,从而建立荷移酶标法测定动物脑脊液和血清中苯巴比妥钠的方法.结果:在水溶液中,苯巴比妥钠与茜素红产生的荷移络合物的最大吸收波长为522 nm,苯巴比妥钠浓度在4~128μmol/L范围内符合比尔定律,蒸馏水组相关系数R~2=0.998,脑脊液组R~2=0.995,血清组R~2=0.991,各实验组线性关系良好.当苯巴比妥钠浓度为64μmol/L时,酶标法9次测定结果的相对标准偏差为0.03%.分光光度法的标准偏差为0.75%.结论:使用酶标法测定脑脊液和血清中的苯巴比妥钠具有操作简便、快速,可行性强,重复性和精密度高的优点,并可实现高通量分析.