PVC膜氯离子选择性电极的制备和尿液中氯离子的测定

以氯离子-三异辛基十六烷基季铵离子缔合物为活性物质,制备了聚氯乙稀(PVC)膜氯离子选择性电极.电极在1.0×10-3～1.0 mol/L范围内呈线性响应关系,检测限为5×10-4 mol/L,响应时间约5 s,漂移小于1 mV/h,平均斜率为47mV/pC.电极的重现性、稳定性良好.采用该电极测定了人造尿液和稀释尿液中氯离子的浓度.用标准加入法,在人造尿液中氯离子的回收率在96.0%～102.5%之间;在稀释尿液中氯离子的回收率在90.3%～98.5%之间.该方法的标准偏差(SD)＜3%,P＜0.05.     

Voltage-dependent translocation of the asialoglycoprotein receptor across lipid membranes

A membrane receptor protein for asialoglycoproteins induces voltage-dependent increases in ion conductance across a lipid bilayer, probably reflecting penetration of the protein into the bilayer towards an electrically positive pole. In the presence of specific ligand for the receptor, this penetration leads to a 'translocation' of the receptor from one side of the bilayer to the other. These observations suggest a mechanism by which biological membranes might regulate the disposition of their proteins, and a way in which membrane receptors involved in endocytosis might be spared lysosomal destruction in order to be recycled to the plasma membrane.     

Effects of lanthanide ions on hydrolysis of phosphatidylinositol in human erythrocyte membranes

The effects of lanthanides on the hydrolysis of phosphatidylinositol in human erythrocyte membranes were studied. ³H-inositol labeling chromatography and HPLC were used to determine inositol 1, 4, 5-triphosphate and diacylglycerol separately, the hydrolytic products of phosphatidylinositol due to the reaction of lanthanide ions with human erythrocyte membranes. The unhydrolyzed phosphatidylinositol in membranes was also determined. The results indicate that the hydrolysis of phosphatidylinositol can be promoted by lanthanides (La³⁺, Ce³⁺, Y³⁺, Tb³⁺) and the effects of La³⁺ and Ce³⁺ are stronger than those of Y³⁺ and Tb³⁺.     

Cyclic peptides-assisted transport of metal ions across liquid-organic membrane

The formation of alkali and alkaline-earth metal picrate complexes with cyclo(Pro-Gly)_n ionophores (1, n = 3; 2, n = 4) can facilitate the migration of metal ions across a bulk liquid CH₂Cl₂ membrane. The migration behavior was studied by measuring the solution absorption at 356 nm, using a UV/Vis spectrophotometer, and the rates can be determined by comparing the initial absorption of donor solutions with the absorption of the corresponding receiver solutions as the function of time. It was found that cyclic peptide 1 shows higher transport activity for the studied alkali and alkaline-earth metal ions than compound 2, which is related to the backbone flexibility of the cyclic peptides. The findings in this work suggest that the rate of ionophore-facilitated ion transport depends not only on the ability of complex formation in aqueous phase, but also on the ability of complex dissociation in organic phase.     

Protein translocation across the eukaryotic endoplasmic reticulum and bacterial plasma membranes

A decisive step in the biosynthesis of many proteins is their partial or complete translocation across the eukaryotic endoplasmic reticulum membrane or the prokaryotic plasma membrane. Most of these proteins are translocated through a protein-conducting channel that is formed by a conserved, heterotrimeric membrane-protein complex, the Sec61 or SecY complex. Depending on channel binding partners, polypeptides are moved by different mechanisms: the polypeptide chain is transferred directly into the channel by the translating ribosome, a ratcheting mechanism is used by the endoplasmic reticulum chaperone BiP, and a pushing mechanism is used by the bacterial ATPase SecA. Structural, genetic and biochemical data show how the channel opens across the membrane, releases hydrophobic segments of membrane proteins laterally into lipid, and maintains the membrane barrier for small molecules.     

几种离子对纤维素酶活力的影响

本文主要研究8种离子对绿色木酶9405所产纤维素酶活力的影响。实验结果表明, Mg2+、Zn2+、Fe2+离子浓度在一定范围内,对纤维素酶活有抑制作用,SeO2-3-在实验浓度范围内对酶活无影响;Cu2+、Mn2+、Co2+、I-等离子浓度在一定范围内,对纤维素酶有激活作用,其中Cu2+激活作用显著,酶活提高30％;8种离子同时使用,激活作用明显,酶活提高幅度达4O％。