NaCl处理对盐地碱蓬开花及Na~+、K~+含量的影响

为探讨盐地碱蓬(Suaeda salsa)开花与盐的关系,研究了1(对照)、200和400 mmol·L-1 NaCl处理对盐地碱蓬不同分枝和单株开花数目、叶片和茎及花器官中的Na+、K+含量及Na+/K+比的影响。结果表明:与对照相比,200 mmol·L-1 NaCl处理下盐地碱蓬分枝及单株开花数目增加最显著,单株开花数目增加了69.90%,花器官中的Na+含量、Na+/K+比分别增加了1.41倍和1.77倍,而一级叶片的Na+含量、Na+/K+比分别增加了3.96倍和4.96倍,茎中Na+含量、Na+/K+比分别增加了7.00倍和12.39倍。400 mmol·L-1 NaCl处理下,单株开花数目增加了19.00%,花器官中的Na+含量、Na+/K+比分别增加了2.09倍和3.21倍,而一级叶片的Na+含量、Na+/K+比分别增加了4.28倍和6.50倍,茎中Na+含量、Na+/K+比分别增加了7.65和15.40倍。这些结果表明,NaCl处理下真盐生植物盐地碱蓬可能通过把Na+区域化到茎叶而动员其中的K+到花器官中维持花器官中合适的Na+/K+比而促进开花。     

不同耐盐性小麦根Na~+和K~+的吸收特性

以耐盐小麦品种‘德抗961’和盐敏感小麦品种‘鲁麦15’为材料,研究小麦根Na+、K+吸收特性及其与耐盐性关系。结果表明,2个小麦品种根K+吸收动力学曲线均符合Michaelis-Menten方程,即V=Vmax×[S]/([S]+Km)+k×[S]。低浓度(低于25mmol·L-1)NaCl处理对根高亲和K+吸收系统转运K+具有促进作用,对耐盐品种‘德抗961’的促进作用更大。小麦根高亲和K+吸收系统是通过K+/H+同向转运,而不是K+/Na+同向转运。NaCl处理对根低亲和K+吸收系统有抑制作用,对盐敏感品种‘鲁麦15’的抑制作用更大。NaCl处理导致2个小麦品种根和叶片中的K+含量显著下降,Na+含量显著升高,但‘德抗961’根和叶片中的K+含量均显著高于‘鲁麦15’,‘德抗961’根中Na+含量显著高于‘鲁麦15’,而其叶片中Na+含量显著低于‘鲁麦15’,从而保证NaCl胁迫下其叶片较高的K+/Na+比。非选择性阳离子通道是小麦根Na+吸收的主要途径,K+通道是Na+吸收的一条重要途径。这些结果表明小麦部分通过调节根系K+吸收系统而维持叶片较高的K+/Na+比,从而提高其耐盐性。     

盐胁迫下水稻苗期Na+和K+吸收与分配规律的初步研究

选择苗期耐盐性较强的水稻(Oryza sativa)品种(株系)'AB52'、'02402'和'02435'及敏感品种'日本晴',在网室周转箱内,设置5 000和8 000 mg·L-1NaCl两种盐处理,以清水为对照,研究盐胁迫下苗期水稻植株不同部位Na+和K+的吸收和分配与品种耐盐性的关系.结果表明,盐胁迫下,株高、绿叶干重和绿叶面积下降,绿叶中的水分含量降低,但茎鞘中的水分含量有所上升.5 000 mg·L-1NaCl胁迫处理10 d,耐盐品种所受的生长影响和叶片伤害程度低于敏感品种,但8 000 mg·L-1NaCl胁迫处理下品种间差异变小.盐胁迫下,水稻植株吸收Na+和置换出K+,但不同器官部位中Na+和K+的区域化分布特征明显,各部位的Na+含量由低到高依次为绿叶、根、茎鞘和枯叶.下部老叶能优先积累较多Na+而枯黄;绿叶吸收Na+相对较少,维持较低的Na+水平,同时保持较高且稳定的K+含量;植株茎鞘通过选择性吸收大量Na+和置换出一部分K+到叶片中,保持绿叶较稳定的K+含量和相对较低的Na+含量,维持较高的K+/Na+比,从而使植株少受盐害.敏感品种'日本晴'在盐胁迫下绿叶中的Na+含量相对较高,且5 000 mg·L-1NaCl胁迫下绿叶Na+含量已接近高值,与在8 000 mg·L-1NaCl胁迫下差异不大,而耐盐品种绿叶吸收较少的Na+.另一方面,耐盐品种茎鞘的含K+相对较高,在盐胁迫下能吸收容纳较多的Na+,而绿叶中K+/Na+比较高.可以认为,绿叶的K+/Na+比可作为一个衡量耐盐性的相对指标.     

NaCl胁迫对4种豆科树种幼苗生长和K~+、Na~+含量的影响

以合欢、刺槐、国槐和皂荚4种豆科树种盆栽实生幼苗为试验材料,研究了NaCl胁迫下4个树种幼苗的生长、耐盐临界浓度和Na+、K+含量的变化,并对其耐盐性进行了比较.结果表明:NaCl胁迫抑制了4个树种幼苗的生长,苗木的干物质积累量减小、根冠比增大,尤其对合欢和皂荚的影响较大;以相对干质量降至对照组50%时的NaCl浓度作为生长临界NaCl浓度(C50)指标,4个树种的耐盐强弱顺序为:刺槐(5.0‰)>国槐(4.5‰)>皂荚(3.9‰)>合欢(3.0‰);随NaCl浓度的增加,各树种幼苗根、茎、叶中Na+含量逐渐增加,K+含量先增加后减小(合欢根除外),而K+/Na+差异较大.相同浓度NaCl胁迫下,幼苗器官的Na+分布为根>茎>叶,K+因树种和NaCl浓度不同而各异,以叶片中较多,K+/Na+为叶>茎>根.NaCl胁迫下,刺槐的K+含量和K+/Na+较高,地上部分Na+含量较低,幼苗干物质量大,耐盐性较强;而合欢的K+/Na+较小,高浓度NaCl胁迫下地上部分的Na+含量较高,幼苗干物质量小,耐盐性较差.苗木地上部分对K+的积累和根部对Na+的滞留是影响豆科树种耐盐性能的主要因素.     

NaCl胁迫下沙枣幼苗生长和阳离子吸收、运输与分配特性

沙枣(Elaeagnus angustifolia L.)耐盐性强,是我国北方生态脆弱地区造林绿化的一个先锋树种。为探讨沙枣的盐适应机制,研究了不同浓度NaCl(0、100和200 mmol/L)胁迫30d对其水培幼苗生物量累积以及不同组织(根、茎、叶)K+、Na+、Ca2+和Mg2+吸收、运输与分配的影响。结果表明:盐胁迫不同程度地促进了沙枣苗根系生长;100 mmol/L NaCl胁迫对幼苗生物量累积无明显影响,而200 mmol/L则显著抑制了生物量累积;盐胁迫幼苗根、茎、叶中Na+含量以及K+-Na+选择性运输系数(S K,Na)和Ca2+-Na+选择性运输系数(S Ca,Na)显著或大幅度增加,而K+、Ca2+、Mg2+含量以及K+/Na+、Ca2+/Na+和Mg2+/Na+比值则显著或大幅度下降;200 mmol/L NaCl胁迫沙枣根Na+含量和根Na+净累积量分别为22.15 mg/g干重和1.87 mg/株(是对照的16.20倍和20.06倍),根成为Na+净累积量增加幅度最大的组织和Na+含量最高的组织;200 mmol/L NaCl胁迫沙枣茎、叶中的Na+含量以及冠组织Na+净累积量分别高达5.15、7.71 mg/g干重和3.29 mg/株(是对照的7.22倍、9.58倍和5.45倍),但幼苗仍能正常生长。综合分析认为,沙枣的盐适应机制是根系拒盐和冠组织耐盐,主要通过根系的补偿生长效应、根系对Na+的聚积与限制作用以及冠组织对Na+的忍耐来实现的,同时也与根、茎和叶对K+、Ca2+选择性运输能力显著增强有关。     

披针叶黄华试管苗适应盐胁迫的渗透调节机制

以披针叶黄华(Thermopsis lanceolata)试管苗为材料,通过组培方法研究其在0、0.2%、0.4%、0.6%、0.8%和1.0%NaCl和Na2SO4胁迫30d后的生长、有机渗透调节物质和无机渗透调节物质(Na+、K+和Ca2+)含量的变化,以探讨其耐盐性机制。结果显示:(1)随NaCl和Na2SO4胁迫浓度的增加,披针叶黄华试管苗叶片脯氨酸和可溶性糖含量均显著持续增加,且NaCl胁迫下脯氨酸上升的幅度均大于相同浓度Na2SO4胁迫下的增幅,而可溶性糖上升的幅度却小于相同浓度Na2SO4胁迫下的幅度;可溶性蛋白含量随NaCl浓度的增大呈先升高后降低的趋势,但随Na2SO4浓度的增加呈持续上升的趋势。(2)随NaCl和Na2SO4浓度的增加,披针叶黄华试管苗Na+含量呈增加趋势且各处理均显著高于对照,Ca2+含量和叶片K+含量却呈逐渐减少趋势且各处理均显著低于对照,而根系K+含量呈先降后升的趋势;Na2SO4胁迫下披针叶黄华试管苗叶片Na+含量上升幅度以及K+和Ca2+含量下降幅度均明显低于相同浓度NaCl胁迫组;而Na+/K+和Na+/Ca2+比值随NaCl和Na2SO4浓度增加而升高;NaCl胁迫下,叶片Na+/K+和Na+/Ca2+高于相同浓度Na2SO4胁迫下的比值,而根系Na+/K+和Na+/Ca2+却低于相同浓度Na2SO4胁迫下的比值。研究表明,盐胁迫下,披针叶黄华试管苗通过抑制叶片中Na+积累并增加可溶性糖和可溶性蛋白含量,在根系中维持较高K+和Ca2+含量以及较低水平Na+/K+和Na+/Ca2+比,以降低披针叶黄华细胞渗透势来适应盐渍环境;披针叶黄华对NaCl胁迫的调节能力弱于Na2SO4。     

不同耐盐性药用甘草幼苗根对Na~+的响应及其维管组织变化

以甘草属2种耐盐植物胀果甘草、乌拉尔甘草为材料,用不同浓度(50、100、150、200、250mmol·L-1)NaCl处理幼苗21d后,分析其生物量和根、茎、叶中的Na+、K+含量以及K+/Na+,计算根的离子选择吸收和运输系数,并应用光学显微镜观察比较二者的维管组织结构变化,以揭示2种药用甘草幼苗根对Na+的响应及其维管组织结构的变化特征,探讨甘草的耐盐机理。结果表明:(1)NaCl胁迫使2种甘草幼苗生物量均下降,在NaCl浓度为250mmol·L-1时,胀果甘草、乌拉尔甘草幼苗生物量分别是对照的53.34%、46.21%,胀果甘草耐盐性强于乌拉尔甘草。(2)随着NaCl浓度上升,2种甘草根积累的Na+显著增多,其中胀果甘草在所有盐处理下,根Na+含量均高于其它器官,说明其根对吸收的Na+具有显著截留效应;而乌拉尔甘草只在0~150mmol·L-1 NaCl范围内,根Na+含量显著高于叶片,当NaCl为200、250mmol·L-1时,叶片Na+含量显著高于根,说明乌拉尔甘草根对Na+的截留能力有限。(3)在相同盐处理下,胀果甘草离子选择吸收系数SAK,Na、离子运输系数STK,Na均大于乌拉尔甘草,胀果甘草根抑制Na+、促进K+向地上部运输的能力强于乌拉尔甘草。(4)乌拉尔甘草在NaCl为150、200mmol·L-1、胀果甘草在250mmol·L-1时,根结构对盐胁迫产生应激性响应,维管组织比例显著上升,有助于提高根向上的运输能力,减少盐害。研究表明,2种药用甘草根对Na+截留作用和向上运输时促K+抑Na+能力的差异,是导致其耐盐能力不同的主要原因,根对Na+的积累和截留作用的差异与根的结构响应相吻合,能较好地解释二者的耐盐性差异。     

NaCl胁迫对2个菊属野生种幼苗体内K~+、Na~+和Cl~-分布及生长的影响

采用营养液水培,研究了不同浓度NaCl处理下耐盐性不同的2个菊属物种幼苗的生长变化及体内K+、Na+、Cl-在器官间的区域化分布和吸收、运输特性,以揭示其耐盐差异机制。结果表明,NaCl胁迫下,2个物种的新生叶面积比率减小,受害叶面积比率增加,叶电解质外渗率增加;大岛野路菊受胁迫影响较轻。2个物种体内Na+和Cl-含量随NaCl浓度的升高而增大,且地上部的Na+、Cl-积累量大于根系,成熟叶是2个物种Na+、Cl-积累的主要器官。新生叶、茎的K+含量也随NaCl浓度的升高而增加。与耐盐性强的大岛野路菊相比,NaCl胁迫下萨摩野菊各器官积累的Na+和Cl-量均显著高于前者,其生长对其体内含有的Na+和Cl-比大岛野路菊更为敏感。除高盐胁迫下的根以外,大岛野路菊各器官的K+/Na+均显著高于萨摩野菊。大岛野路菊根向茎运输的SK,Na值远高于萨摩野菊,茎向中位成熟叶运输的SK,Na值较低,高盐胁迫时茎向上位新生叶运输的SK,Na值较高。说明NaCl胁迫下大岛野路菊对Cl-、Na+的累积能力弱、维持K+、Na+平衡的能力强,且根系对Na+的截留能力强,茎向上位新生叶运输Na+的选择性较低,是其耐盐性强的主要原因,而茎向中位成熟叶运输Na+的选择性较高是其对盐胁迫的适应。多元回归分析结果还表明,Cl-对萨摩野菊的影响强于Na+。     

NaCl处理对西伯利亚白刺幼苗生长及离子平衡的影响

以1年生西伯利亚白刺水培幼苗为材料,研究了不同浓度NaCl(0、200、400mmol·L~(-1))处理对幼苗生长及不同器官(根、茎、叶)中Na~+、K~+、Ca~(2+)、Mg~(2+)的吸收、运输与分配的影响,探讨西伯利亚白刺的盐适应机制。结果表明:(1)200mmol·L~(-1) NaCl处理促进了西伯利亚白刺幼苗的生长及叶片肉质化程度,400mmol·L-1 NaCl处理显著抑制其生长。(2)随着NaCl处理浓度的升高,西伯利亚白刺幼苗根、茎、叶中Na~+含量显著增加,且叶中Na~+含量显著高于茎和根中;根系中K~+含量显著增加;根、茎、叶中Ca~(2+)、Mg~(2+)含量在200mmol·L~(-1) NaCl处理下保持平稳或上升,而在400mmol·L-1 NaCl处理下显著下降。(3)各器官中K~+/Na~+、Ca~(2+)/Na~+和Mg~(2+)/Na~+比值总体随NaCl处理浓度的升高呈下降趋势,且根部离子比值始终高于叶片和茎。(4)随着NaCl处理浓度的升高,西伯利亚白刺幼苗根-茎SK,Na显著下降,而根-茎SCa,Na、SMg,Na及茎-叶SK,Na、SCa,Na、SMg,Na逐渐提高。研究发现,西伯利亚白刺的盐适应机制主要是通过植株的补偿生长效应及叶片对Na~+的聚积作用实现的,同时也与根系对K~+的扣留及茎叶对K~+、Ca~(2+)、Mg~(2+)选择性运输能力增强有关。     

花期海蓬子对盐胁迫的生理响应

研究了花期阶段不同浓度NaCl(0、10‰、20‰、30‰、40‰、50‰和60‰)对海蓬子(Salicornia bigelovii)生长、光合色素、光合作用参数、抗氧化和离子含量的影响.结果表明:10‰NaCl盐处理下海蓬子株高、茎生物量、叶绿素(Chl)含量、净光合速率(Pn)、气孔导度(Gs)、蒸腾速率(Tr)、胞间CO2浓度(Ci)、茎SOD活性和POD活性等指标值均显著高于其它处理,而高盐(40‰NaCl及其以上)胁迫下,上述指标值均表现为下降,同时茎K+含量也显著下降,而茎Na+、Cl、Na+/K+和MDA含量等显著上升.相关分析显示,生物量与Chl a/Chl b呈现显著正相关,与株高、茎Pn、Gs、Ci、Chl、Chl含量、K+含量、SOD和POD活性呈现极显著正相关,与气孔限制值(Ls)、Car/Chl、MDA含量、Cl含量和Na+/K+等均呈极显著负相关.综上所述,10‰NaCl处理是花期海蓬子生长和光合生长的最适宜盐度,而无盐和高盐下海蓬子光合抑制主要是来自气孔因素,同时高盐胁迫下还伴随着非气孔限制.     

玉米籽粒重金属铅(Pb2+)含量的QTL定位

铅(Pb²⁺)是现存环境最大量的有毒重金属污染元素,在我国特别是西南地区种植的玉米受重金属Pb²⁺污染日益严重,已严重影响到食物安全。文章利用玉米籽粒Pb²⁺低富集自交系178和籽粒Pb²⁺高富集自交系9782杂交衍生的重组自交系群体为作图群体,利用165对SSR多态性标记,构建了总长度为1499.85 cM、标记间平均距离为9.07 cM的分子遗传图谱,对玉米籽粒Pb²⁺含量性状进行了QTL定位分析,以期为选育籽粒低富集Pb²⁺的玉米新品种提供参考。结果表明,在Pb²⁺浓度为333.32 mg/kg胁迫下,共检测到2个与籽粒Pb²⁺含量相关的QTL,分别位于玉米第1、第4号染色体,其中qPC1位于标记区间umc1661~phi002h之间,表型贡献率为11.13%,加性效应为0.062;qPC4位于umc1117~nc005之间,表型贡献率为5.55%,加性效应为-0.044。性状相关分析结果表明,籽粒中Pb²⁺含量与穗长、穗粗、行粒数、穗重和百粒重等产量性状间均未达到显著水平,表明选育玉米籽粒Pb²⁺低富集的新自交系或杂交种不一定会影响到产量性状,而且籽粒Pb²⁺含量是一个相对独立的遗传性状。     

Effects of Systemic Kainic Acid Administration on Regional Na+, K+-ATPase Activity in Rat Brain

Changes in the activity of Na+,K+-ATPase and in the water, Na+, and K+ levels in the parietal cortex, hippocampus, and thalamus were investigated in rats 1, 3, 6, and 24 h following systemic kainic acid injection. An increase in Na+,K+-ATPase activity was observed in all three regions 3 h after the treatment, with a subsequent decrease in enzyme activity. The elevation in Na+,K+-ATPase activity was accompanied by an increase in the Na+ content and a decrease in the K+ content. These changes are presumed to occur because of repeated discharges and excessive prolonged depolarization in response to kainic acid. The decreases in Na+,K+-ATPase activity 6 and 24 h following kainic acid treatment coincide with neuropathological damage and edema formation, mainly in the hippocampus and thalamus.     

FramePlot: a new implementation of the Frame analysis for predicting protein-coding regions in bacterial DNA with a high G+C content

FramePlot is a web-based tool for predicting protein-coding regions in bacterial DNA with a high G + C content, such as Streptomyces. The graphical output provides for easy distinction of protein-coding regions from non-coding regions. The plot is a clickable map. Clicking on an ORF provides not only the nucleotide sequence but also its deduced amino acid sequence. These sequences can then be compared to the NCBI sequence database over the Internet. The program is freely available for academic purposes at http://www.nih.go.jp/jun/cgi-bin/frameplot.pl.     

The Ca 2+ pumps and the Na + / Ca 2+ exchangers

The Ca 2+ ATPases or Ca 2+ pumps transport Ca 2+ ions out of the cytosol, by using the energy stored in ATP. The Na + / Ca 2+ exchanger uses the chemical energy of the Na + gradient (the Na + concentration is much higher outside than inside the cell) to remove Ca 2+ from the cytosol. Ca 2+ pumps are found in the plasma membrane and in the endoplasmic reticulum of the cells. The pumps are probably present in the membrane of other organelles, but little experimental information is available on this matter. The Na + / Ca 2+ exchangers are located on the plasma membrane. A Na + / Ca 2+ exchanger was found in the mitochondria, but very little is known on its structure and sequence. These transporters control the Ca 2+ concentration in the cytosol and are vital to prevent Ca 2+ overload of the cells. Their activity is controlled by different mechanisms, that are still under investigation. A number of the possible isoforms for both types of proteins has been detected.© Kluwer Academic Publishers     

高活性Co2+替代海因酶中Co2+的定量及酶学活性鉴定

利用产D-海因酶(HDT)的重组pE-hdt/E.coli菌株,在LB培养基中添加40μmol/L的Co2+,37℃培养10 h, 表达产物经Q-Sepharose 阴离子交换剂和Phenyl-Sepharose疏水层析,获得电泳纯Co2+D-海因酶(Co2+-HDT).该酶对底物DL-海因的比活性较HDT高约6倍,达21.8 U/mg.可见光光谱分析表明,在498 nm和568 nm处呈现Co2+海因酶络合物的特征性吸收峰.用ICP-AES测定纯酶金属离子含量,HDT每摩尔亚基含0.93摩尔Zn2+和0.04摩尔Co2+,而Co2+-HDT中每摩尔亚基中含0.17摩尔Zn2+ 和089摩尔Co2+.这一结果表明,HDT中的Zn2+ 已被Co2+所替代.此外,在动力学常数,pH和温度稳定性,金属螯合剂EDTA的影响等方面,HDT和Co2+-HDT也略有差异.     

Cardiac sarcolemmal Na+-Ca2+ exchange and Na+-K+ ATPase activities and gene expression in alloxan-induced diabetes in rats

To determine the sequence of alterations in cardiac sarcolemmal (SL) Na⁺-Ca²⁺ exchange, Na⁺-K⁺ ATPase and Ca²⁺-transport activities during the development of diabetes, rats were made diabetic by an intravenous injection of 65 mg/kg alloxan. SL membranes were prepared from control and experimental hearts 1-12 weeks after induction of diabetes. A separate group of 4 week diabetic animals were injected with insulin (3 U/day) for an additional 4 weeks. Both Na⁺-K⁺ ATPase and Ca²⁺-stimulated ATPase activities were depressed as early as 10 days after alloxan administration; Mg²⁺ ATPase activity was not depressed throughout the experimental periods. Both Na⁺-Ca²⁺ exchange and ATP-dependent Ca²⁺-uptake activities were depressed in diabetic hearts 2 weeks after diabetes induction. These defects in SL Na⁺-K⁺ ATPase and Ca-transport activities were normalized upon treatment of diabetic animals with insulin. Northern blot analysis was employed to compare the relative mRNA abundances of _--subunit of Na⁺-K⁺ ATPase and Na⁺-Ca²⁺ exchanger in diabetic ventricular tissue vs. control samples. At 6 weeks after alloxan administration, a significant depression of the Na⁺-K⁺ ATPase _-- subunit mRNA was noted in diabetic heart. A significant increase in the Na⁺-Ca²⁺ exchanger mRNA abundance was observed at 3 weeks which returned to control by 5 weeks. The results from the alloxan-rat model of diabetes support the view that SL membrane abnormalities in Na⁺-K⁺ ATPase, Na⁺Ca²⁺ exchange and Ca²⁺-pump activities may lead to the occurrence of intracellular Ca²⁺ overload during the development of diabetic cardiomyopathy but these defects may not be the consequence of depressed expression of genes specific for those SL proteins.     

A new value for mol percent guanine + cytosine of DNA for the salmonid fish pathogen Renibacterium salmoninarum

The mol% G + C of DNA extracted from seven different isolates of Renibacterium salmoninarum was determined. Organisms studied were from selected geographical areas (U.S.A., Canada, England and France) and were isolated from five different species of salmonid fish. The mol% G + C was determined to be 55.5, higher than the currently reported value of 53.     

The gene sll0273 of the cyanobacterium Synechocystis sp. strain PCC6803 encodes a protein essential for growth at low Na+/K+ ratios

A mutant of Synechocystis sp. strain PCC6803 was obtained by random cartridge mutagenesis, which could not grow at low sodium concentrations. Genetic analyses revealed that partial deletion of the sll0273 gene, encoding a putative Na ⁺ /H ⁺ exchanger, was responsible for this defect. Physiological characterization indicated that the sll0273 mutant exhibited an increased sensitivity towards K ⁺ , even at low concentrations, which was compensated for by enhanced concentrations of Na ⁺ . This enhanced Na ⁺ demand could also be met by Li ⁺ . Furthermore, addition of monensin, an ionophore mediating electroneutral Na ⁺ /H ⁺ exchange, supported growth of the mutant at unfavourable Na ⁺ /K ⁺ ratios. Measurement of internal Na ⁺ and K ⁺ contents of wild‐type and mutant cells revealed a decreased Na ⁺ /K ⁺ ratio in mutant cells pre‐incubated at a low external Na ⁺ /K ⁺ ratio, while it remained at the level of the wild type after pre‐incubation at a high external Na ⁺ /K ⁺ ratio. We conclude that the Sll0273 protein is required for Na ⁺ influx, especially at low external Na ⁺ concentrations or low Na ⁺ /K ⁺ ratios. This system may be part of a sodium cycle and may permit re‐entry of Na ⁺ into the cells, if nutrient/Na ⁺ symporters are not functional or operating.     

Active calcium transport via coupling between the enzymatic and the ionophoric sites of Ca2+ + Mg2+-ATPase

The 20K dalton fragment of Ca²⁺ + Mg²⁺-ATPase obtained from the tryptically digested sarcoplasmic reticulum has been further purified using Bio-Gel P-100. This removed low-molecular-weight UV-absorbing and positive Lowry-reacting contaminants. The ionophoric activity of the 20K fragment in both oxidized cholesterol and phosphatidylcholine: cholesterol membranes is unaltered by this further purification. The 20K selectivity sequence in phosphatidylcholine: cholesterol membranes is Ba²⁺ > Ca²⁺ > Sr²⁺ > Mn²⁺ Mg²⁺. Digestion of intact sarcoplasmic reticulum vesicles with trypsin, which results in the dissection of the hydrolytic site (30K) from the ionophoric site (20K), is shown to disrupt energy transduction between ATP hydrolysis and calcium transport. This further implicates the 20K dalton fragment as a calcium transport site. These data and previous evidence are discussed in terms of a proposed model for the ATPase molecular structure and the mechanism of cation transport in sarcoplasmic reticulum.     

番茄碱对人红细胞膜Na+-K+-ATPase活性影响的研究

以低渗法从新鲜健康人红细胞中制得膜Na^ -K^ -ATPase,研究了番茄碱(tomatine)X~人红细胞膜Na^ -K^ -ATPase活性的影响。实验结果表明,反应体系中的tomatine浓度低于1mmol／L时,对不依赖钙调蛋白(CAM)激活的Na^ -K^ -ATPase(称之为基本酶活)影响不大,浓度达1mmol／L时,该酶活性仍保持在95％左右;而在此浓度范围内,tomatine对依赖CaM的Na^ -K^ -ATPase有明显的抑制作用,其IC50值为0．16mmol／L．说明tomatine对膜酶Na^ -K^ -ATPase活性的影响可能是通过阻断CaM激活的途径而起作用,从而为进一步研究番茄碱的作用机制奠定了基础。