Calcium-activated potassium channels expressed from cloned complementary DNAs.

Calcium-activated potassium channels were expressed in Xenopus oocytes by injection of RNA transcribed in vitro from complementary DNAs derived from the slo locus of Drosophila melanogaster. Many cDNAs were found that encode closely related proteins of about 1200 aa. The predicted sequences of these proteins differ by the substitution of blocks of amino acids at five identified positions within the putative intracellular region between residues 327 and 797. Excised inside-out membrane patches showed potassium channel openings only with micromolar calcium present at the cytoplasmic side; activity increased steeply both with depolarization and with increasing calcium concentration. The single-channel conductance was 126 pS with symmetrical potassium concentrations. The mean open time of the channels was clearly different for channels having different substituent blocks of amino acids. The results suggest that alternative splicing gives rise to a large family of functionally diverse, calcium-activated potassium channels.     

Resolution and stability of oxazepam enantiomers

A solvent mixture containing dioxane, acetonitrile, and hexane was found to be suitable as a mobile phase to resolve oxazepam enantiomers by chiral stationary phase high performance liquid chromatography using covalent Pirkle columns. The resolved oxazepam enantiomers in this solvent mixture had a racemization half-life greater than 3 days at 23°C. When desiccated at 0°C as dried residue, OX enantiomers were stable for at least 50 days with less than 2% racemization. The conditions which stabilized OX enantiomers significantly facilitated the determination of racemization half-lives of OX enantiomers in a variety of aqueous and nonaqueous solvents and at different temperatures. © 1992 Wiley-Liss, Inc.     

六种鱼腥藻在大量培养中的生产率和适应性与营养成分比较

连续两年对鱼腥藻的六个品系进行了大量培养比较研究,在长江中下游气候条件下,HB1042和HB1105具有稳定的生产性能,5月下旬至九月中旬123d内,平均有效生长分别为114和100d;其次是HB1058,HB686和HB1017,平均有效生长天分别为73,58和71d;HB13适应性较差。生物量生产率在5月下旬、6月中旬至9月中旬较高,除HB13外,平均都在10g干重/m~2/d以上或接近10g/m~2/d。在不同的季节它们表现出了各自的最高生物量生产率。据此,提出了逐月逐旬采取藻种搭配生产,以获得最高生物量生产率的配合关系。营养成分分析表明它们的蛋白质含量在40％左右;氨基酸组成合理,除某些种类的含硫氨基酸略低外,都符合FAO/WHO的标准。     

用纸浆代棉花合成CMC

羧甲基纤维素(CMC)系天然纤维素的衍生物。它是由天然纤维素分子上引入强极性羧甲基钠而得到的。我们采用纸浆为原料替代棉花生产CMC,测试了其性能,并讨论了反应温度、反应时间和碱用量对粘度的影响。结果表明:此法简化了工艺,原料来源广泛,产品性能优良,成本低,能满足使用要求。