外界因子对条斑紫菜自由壳孢子囊枝形成和生长影响

主要研究了不同光照周期(8L:16d、12L:12d和16L:8d)、不同温度(15℃、20℃和25℃)、不同光照强度(29、42、57、72和86μmol m-2·s-1)等外界因子对条斑紫菜自由丝状藻丝切断诱导形成壳孢子囊枝影响,以期获得条斑紫菜壳自由孢子囊枝形成的最佳外界条件.结果表明,在25℃和57μmol m-2·s-1条件培养30d后,短日照(8L:16d)对壳孢子囊枝诱导形成效果最好,其壳孢子囊枝形成率高迭92,5%,50d后几乎达到100%;在25℃和短日照条件培养30d后,光照强度为57μmol m-2·s-1,时,壳孢子囊枝诱导形成率达到最高(92.2%),光照强度过高过低均不利壳孢子囊枝形成;在57μmol m-2·s-1和短日照条件下,当温度为25℃时,壳孢子囊枝形成率最高,形成率随温度下降而减少.在12L:12d光照周期、57μmol m-2·s-1光照强度和25℃温度条件下,自由壳孢子囊枝生长最快,其日平均相对生长率可迭54.43%.以上研究为实现紫菜细胞工程育苗新技术一自由壳孢子囊枝育苗奠定了坚实基础.     

几种主要环境因子对布朗葡萄藻(Botryococcus braunii)光合作用的影响

利用测定净光合放氧速率的方法研究了光照强度、温度、 pH值、盐度对布朗葡萄藻Botryococcus braunii UTEX 572和B.braunii UTEX 2441两个品系的光合作用的影响.B.braunii UTEX 572的适宜光照强度范围400～1600 μmol·m-2·s-1,光饱和点在800 μmol·m-2·s-1附近;适宜温度范围25～35℃,最适温度30℃;适宜pH范围5.0～8.0,最适pH7.0;适宜盐度范围0～0.2 mol/L,最适盐度0.1mol/L.B.braunii UTEX 2441的适宜光照强度范围400～1600 μmol·m-2·s-1,光饱和点在400 μmol·m-2·s-1附近;适宜温度范围25～35℃,最适温度30℃;适宜pH范围5.0～8.0,最适pH 7.0;对盐度的适应范围较小,盐度升高,光合放氧速率明显下降.两个布朗葡萄藻净光合放氧速率随光照强度、温度、pH值和盐度变化的规律,表明布朗葡萄藻的基本生理生态学特征:适应于较强的光照强度、较高的温度、中性偏酸的环境和较低的盐度.对布朗葡萄藻基本生理生态学特征的了解,为培养条件的优化提供了依据.2个布朗葡萄藻品系对光强、温度、pH值和盐度变化的反应有所不同:与B.braunii UTEX 2441相比,B.braunii UTEX 572具有更高的光饱和点,适应更高的温度,对pH值变化有更宽的适应范围,适当提高盐度对其光合作用有促进作用,表明B.braunii UTEX 572在快速生长繁殖方面具有更大的潜力,这一研究结果为筛选适合于大量培养的优良藻种提供了依据.     

环境因子对小球藻(Chlorella sp.XQ-20044)光合作用的影响

小球藻(Chlorella sp.XQ-20044)是一株具有应用潜力的产油微藻,本文利用测定净光合放氧速率的方法研究了光照强度、温度、pH值和盐度对其光合作用的影响。研究结果表明:小球藻适宜的光照强度为500~1200μmol·m-2·s-1,光补偿点约30μmol·m-2·s-1,光饱和点在600μmol·m-2·s-1附近;光合作用适宜的温度范围为30~42.5℃,最适温度为40℃;适宜的pH值范围7.0~10.0,最适pH值为8.0;适宜盐度范围0.1~0.3 mol/L,最适盐度为0.2 mol/L。从光合作用特性来看,小球藻能适应较强的光照强度、较高的温度、偏碱性和较高的盐度环境,其中可耐受较高盐度的特性,有助于预防敌害生物的污染,对于实现规模培养,特别是利用开放系统进行规模培养较为有利。     

温、光、盐对三角褐指藻紫外诱变株生长、总脂及脂肪酸的影响

为了优化微藻培养条件,采用单因子试验研究了不同温度(10、15、20、25、30℃)、不同光照强度(20、40、60、80、100、120μmol·m-2·s-1)和不同盐度(5、10、15、20、25、30、35、40)对三角褐指藻紫外诱变株MP-2的影响。结果表明:温、光、盐对MP-2的生长、总脂含量和脂肪酸组成影响显著(P0.05)。MP-2生长和总脂积累的适宜温度为10~25℃,最适20℃;低温有利于EPA和PUFA的积累,15℃时EPA(30.94%)和PUFA(39.53%)较高;MP-2生长的适宜光照强度为20~120μmol·m-2·s-1,最适光强为40μmol·m-2·s-1,低光强有利总脂的积累,光照强度为20~40μmol·m-2·s-1时总脂含量(25.81%~25.26%)较高;光强对PUFA和EPA的积累影响显著(P0.05),光照强度100μmol·m-2·s-1时EPA高达29.15%,光照强度80~100μmol·m-2·s-1时PUFA高达40.22%~40.56%;MP-2生长的适宜盐度为10~40,最适盐度25,高盐有利总脂的积累,盐度30~35时总脂含量高达36.54%~36.66%,低盐有利EPA和PUFA积累,盐度为10~15时EPA高达31.31%~31.46%,盐度15时PUFA最高(44.75%)。     

固定化微绿球藻去除NH4+-N、PO43——P效果的研究

为了探究固定化微绿球藻（Nannochloropsis oculata）去除污水中NH4+-N、PO43--P的效果,采用海藻酸钠固定化包埋技术进行实验。开展了固定化藻球大小、藻细胞包埋密度、藻球投放质量及充气培养条件对NH4+-N、PO43--P去除效果的单因子试验研究。结果表明,固定化藻球大小、藻细胞包埋密度、藻球投放质量和充气培养条件对NH4+-N、PO43--P的去除效果影响显著（P0.05）。藻球直径3.5 mm时生长速率（K）值最大（0.3320.002）,同时NH4+-N、PO43--P去除率效果最佳,分别为（75.083.83）%和（80.803.81）%;藻细胞包埋密度100104 cells/ball时K值最大（0.3300.033）,而NH4+-N、PO43--P去除率则以藻细胞包埋密度300104 cells/ball组为佳,分别达（87.200.43）%和（82.581.72）%,但考虑单位藻细胞去除率,包埋密度以100104 cells/ball为宜;随着藻球用量的增加K值下降,10 g/L组K值最大（0.3010.02）、50 g/L组K值最小（0.1930.01）,投放量30和50 g/L时NH4+-N去除率较高分别为（84.120.78）%和（84.630.45）%,30 g/L组PO43--P去除率最高达（77.131.43）%。综合考虑,藻球投放量选用30 g/L为宜;充气条件培养K值、NH4+-N和PO43--P去除率显著（P0.05）高于不充气,K值分别为（0.3060.006）和（0.1770.010）;NH4+-N去除率分别为（85.930.45）%和（49.320.45）%;PO43--P去除率分别为（66.665.00）%和（46.292.12）%。研究优化了微绿球藻固定化条件:固定化微绿球藻应进行充气培养,藻球规格3.5 mm、藻细胞包埋密度100104 cells/ball、藻球投放量30 g/L。     

藓羽藻的组织培养和快速繁殖

1植物名称藓羽藻(Bryopsis hypnoides). 2材料类别叶状体片段. 3培养条件培养基均为高压灭菌的天然海水,内含0.1mol·L-1NaNO3和0.1 mol·L-1NH3H2PO4.诱导分化的条件为:温度18℃,光照度15 μmol·m-2·s-1,光照时间12 h·d-1.移植后的培养条件为:温度18℃,光照强度20～50μmol·m-2·s-1,光照时间8 h·d-1.     

单生卵囊藻(Oocystis solitaria)和月牙藻(Selenastrumsp.)的培养条件及其细胞组成

从海滨的淡水池沼中分离得到单生卵囊藻(Oocystis solitaria)和月牙藻(Selenastrum sp.),分别研究了温度、光照强度、盐度对2种微藻生长繁殖的影响,分析了2种微藻的细胞组成、脂肪酸组成及盐度对2种微藻脂肪积累的影响.结果表明:单生卵囊藻和月牙藻的适宜生长温度分别为35.9℃～40.5℃和29.7℃～32.8℃;单生卵囊藻和月牙藻的适宜光照强度分别为46～70μmol · m-2·s-1和17 ～54 μmol·m-2·s-1;单生卵囊藻在淡水培养液中生长最好,月牙藻在盐度为2的半成水培养液中生长最好;在适宜培养条件下,单生卵囊藻细胞蛋白、总糖和总脂肪分别为27.61％、22.00％和3.84％;月牙藻细胞的蛋白、总糖和总脂肪分别为28.06％、21.99％和12.53％;单生卵囊藻的脂肪酸组成中含有丰富的18∶3n3;月牙藻的脂肪酸组成中含有DHA;盐度影响2种微藻的总脂肪含量;单生卵囊藻和月牙藻分别在盐度4和10的半咸水培养液中细胞总脂含量最高.     

不同培养条件对枝鞘藻生长、虾青素和油脂积累的影响

以丝状绿藻枝鞘藻(Oedocladium sp.)为实验材料,研究在100、300μmol·m-2·s-1和双侧300μmol·m-2·s-13种光强以及1、3、9、18 mmol/L 4种初始氮浓度下,两步法培养(第12 d时实验组分别更换为无氮培养基及加盐培养基)对枝鞘藻生长、油脂和虾青素积累的影响。结果显示:枝鞘藻最大生物量在双侧300μmol·m-2·s-1光强,18 mmol/L初始氮浓度更换为无氮培养基的条件下达到,为9.61 g/L;最高虾青素含量和最高油脂含量在双侧300μmol·m-2·s-1光强,3 mmol/L初始氮浓度更换为加盐培养基条件下达到,分别达到干重的1.62%和51.19%。研究结果表明高光条件有利于枝鞘藻的生长,双侧高光条件下低氮浓度更换为加盐培养基最有利于枝鞘藻虾青素和油脂的积累。     

光照强度、温度、pH、盐度对小球藻（Chlorella）光合作用的影响

利用测定净光合放氧速率的方法研究了光照强度、温度、pH、盐度对小球藻（Chlorella sp.XQ-200419）和海洋小球藻（Chlorella marina NJ-016）光合作用的影响。小球藻（Chlorella sp.XQ-200419）的适宜光照强度范围为100～〉1600μmo·lm-2·s-1,光饱和点在500μmo·lm-2·s-1附近;适宜温度范围为25～42.5℃,最适温度为37.5℃;适宜pH值范围为6.5～9.0,最适pH值为7.0;对盐度的适应范围较广,在0～0.6mol/L范围内,随着盐度的升高,净光合放氧速率有下降趋势。海洋小球藻（Chlorella marina NJ-016）的适宜光照强度范围为400～〉1600μmol·m-2·s-1,光饱和点在1400μmo·lm-2.s-1附近;适宜温度范围为25～42.5℃,最适温度为37.5℃;适宜pH值范围为5.0～9.0,最适pH值为8.0;对盐度有很好的适应性,在0～0.6mol/L范围内,随着盐度升高,净光合放氧速率明显上升。小球藻和海洋小球藻的净光合放氧速率随光照强度、温度、pH值和盐度变化的规律,表明了两种小球藻的基本生理生态学特性：能适应较强的光照强度、较高的温度、中性偏碱的环境和较高的盐度。研究结果有助于小球藻培养条件的优化。两种小球藻对光照强度、温度、pH值和盐度变化的反应也有所不同：与小球藻（Chlorella sp.XQ-200419）相比,海洋小球藻（Chlorella marina NJ-016）对光照强度有更好的适应性,对pH值变化有更宽的适应范围,适当提高盐度对其光合作用有明显的促进作用。这表明海洋小球藻（Chlorella marina NJ-016）在快速生长繁殖方面具有更大的潜力,这一研究结果为筛选适合于大量培养的优良藻种提供了依据。     

光照强度、温度、pH、盐度对小球藻(Chlorella)光合作用的影响

利用测定净光合放氧速率的方法研究了光照强度、温度、pH、盐度对小球藻(Chlorella sp.XQ-200419)和海洋小球藻(Chlorella marina NJ-016)光合作用的影响。小球藻(Chlorella sp.XQ-200419)的适宜光照强度范围为100～1600μmo·lm-2·s-1,光饱和点在500μmo·lm-2·s-1附近;适宜温度范围为25～42.5℃,最适温度为37.5℃;适宜pH值范围为6.5～9.0,最适pH值为7.0;对盐度的适应范围较广,在0～0.6mol/L范围内,随着盐度的升高,净光合放氧速率有下降趋势。海洋小球藻(Chlorella marina NJ-016)的适宜光照强度范围为400～1600μmol·m-2·s-1,光饱和点在1400μmo·lm-2.s-1附近;适宜温度范围为25～42.5℃,最适温度为37.5℃;适宜pH值范围为5.0～9.0,最适pH值为8.0;对盐度有很好的适应性,在0～0.6mol/L范围内,随着盐度升高,净光合放氧速率明显上升。小球藻和海洋小球藻的净光合放氧速率随光照强度、温度、pH值和盐度变化的规律,表明了两种小球藻的基本生理生态学特性:能适应较强的光照强度、较高的温度、中性偏碱的环境和较高的盐度。研究结果有助于小球藻培养条件的优化。两种小球藻对光照强度、温度、pH值和盐度变化的反应也有所不同:与小球藻(Chlorella sp.XQ-200419)相比,海洋小球藻(Chlorella marina NJ-016)对光照强度有更好的适应性,对pH值变化有更宽的适应范围,适当提高盐度对其光合作用有明显的促进作用。这表明海洋小球藻(Chlorella marina NJ-016)在快速生长繁殖方面具有更大的潜力,这一研究结果为筛选适合于大量培养的优良藻种提供了依据。     

Photosynthesis and apparent affinity for dissolved inorganic carbon by cells and chloroplasts of Chlamydomonas reinhardtii grown at high and low CO2 concentrations

Chloroplasts with high rates of photosynthetic O₂ evolution (up to 120 mol O₂· (mg Chl)^-1·h^-1 compared with 130 mol O₂· (mg Chl)^-1·h^-1 of whole cells) were isolated from Chlamydomonas reinhardtii cells grown in high and low CO₂ concentrations using autolysine-digitonin treatment. At 25° C and pH=7.8, no O₂ uptake could be observed in the dark by high- and low-CO₂ adapted chloroplasts. Light saturation of photosynthetic net oxygen evolution was reached at 800 mol photons·m^-2·s^-1 for high- and low-CO₂ adapted chloroplasts, a value which was almost identical to that observed for whole cells. Dissolved inorganic carbon (DIC) saturation of photosynthesis was reached between 200–300 M for low-CO₂ adapted chloroplasts, whereas high-CO₂ adapted chloroplasts were not saturated even at 700 M DIC. The concentrations of DIC required to reach half-saturated rates of net O₂ evolution (K_m(DIC)) was 31.1 and 156 M DIC for low- and high-CO₂ adapted chloroplasts, respectively. These results demonstrate that the CO₂ concentration provided during growth influenced the photosynthetic characteristics at the whole cell as well as at the chloroplast level.Abbreviations Chl chlorophyll - DIC dissolved inorganic carbon - K_m(DIC) coneentration of dissolved inorganic carbon required for the rate of half maximal net O₂ evolution - PFR photon fluence rate - SPGM silicasol-PVP-gradient medium     

Effects of macro elements and nitrogen source on adventitious root growth and ginsenoside production in ginseng (Panax ginseng C. A. Meyer)

We investigated the effects on ginseng adventitious root growth and ginsenoside production when macro-element concentrations and nitrogen source were manipulated in the culture media. Biomass growth was greatest in the medium supplemented with 0.5-strength NH₄PO₃, whereas ginsenoside accumulation was highest (9.90 mg g^-1 DW) in the absence of NH₄PO₃. At levels of 1.0-strength KNO₃, root growth was maximum, but a 2.0 strength of KNO₃ led to the greatest ginsenoside content (9.85 mg g^-l). High concentrations of MgSO₄ were most favorable for both root growth and ginsenoside accumulation (up to 8.89 mg g^-1 DW). Root growth and ginsenoside content also increased in proportion to the concentration of CaCI₂ in the medium, with the greatest accumulation of ginsenoside (8.91 mg g^-1 DW) occurring at a 2.0 strength. The NH₄/NO₃ ^-- ratio also influenced adventitious root growth and ginsenoside production; both parameters were greater when the NO₃ ^- concentration was higher than that of NH₄ ⁺. Maximum root growth was achieved at an NH₄ ⁺/NO₃ ^- ratio of 7.19/18.50, while ginsenoside production was greatest (83.37 mg L^-1) when NO₃ ^- was used as the sole N source.     

Heme-heme and heme-ligand interactions in the di-heme oxygen-reducing site of cytochrome bd from Escherichia coli revealed by nanosecond absorption spectroscopy

Cytochrome bd is a terminal quinol:O₂ oxidoreductase of respiratory chains of many bacteria. It contains three hemes, b₅₅₈, b₅₉₅, and d. The role of heme b₅₉₅ remains obscure. A CO photolysis/recombination study of the membranes of Escherichia coli containing either wild type cytochrome bd or inactive E445A mutant was performed using nanosecond absorption spectroscopy. We compared photoinduced changes of heme d-CO complex in one-electron-reduced, two-electron-reduced, and fully reduced states of cytochromes bd. The line shape of spectra of photodissociation of one-electron-reduced and two-electron-reduced enzymes is strikingly different from that of the fully reduced enzyme. The difference demonstrates that in the fully reduced enzyme photolysis of CO from heme d perturbs ferrous heme b₅₉₅ causing loss of an absorption band centered at 435 nm, thus supporting interactions between heme b₅₉₅ and heme d in the di-heme oxygen-reducing site, in agreement with previous works. Photolyzed CO recombines with the fully reduced enzyme monoexponentially with τ ∼ 12 μs, whereas recombination of CO with one-electron-reduced cytochrome bd shows three kinetic phases, with τ ∼ 14 ns, 14 μs, and 280 μs. The spectra of the absorption changes associated with these components are different in line shape. The 14 ns phase, absent in the fully reduced enzyme, reflects geminate recombination of CO with part of heme d. The 14-μs component reflects bimolecular recombination of CO with heme d and electron backflow from heme d to hemes b in ∼ 4% of the enzyme population. The final, 280-μs component, reflects return of the electron from hemes b to heme d and bimolecular recombination of CO in that population. The fact that even in the two-electron-reduced enzyme, a nanosecond geminate recombination is observed, suggests that namely the redox state of heme b₅₉₅, and not that of heme b₅₅₈, controls the pathway(s) by which CO migrates between heme d and the medium.     

Utilization of nitrite and nitrate by dwarf bean

The uptake and conversion of NO ₂ ^- and the effect of NO ₂ ^- on the uptake and reduction of NO ₃ ^- were examined in N-depleted Phaseolus vulgaris L. Nitrite uptake at 0.1 mmol dm^-3 was against an electrochemical gradient and became constant after one or two initial phases. Steadystate uptake declined with increasing ambient NO ₂ ^- concentration (0–0.7 mmol dm^-3). In this concentration range root oxygen consumption was unaffected by NO ₂ ^- , indicating that the decrease of NO ₂ ^- uptake was not related to respiration. After 6 h NO ₂ ^- supply, about one-third of the absorbed NO ₂ ^- had accumulated, mainly in the root system. Oxidation of NO ₂ ^- to NO ₃ ^- was not observed. The apparent induction period for NO ₃ ^- uptake was about 6 h in control plants and 3.5 h in plants that were pretreated for 18 h with NO ₂ ^- . In contrast, the time course of NO ₂ ^- uptake was unaffected by pretreatment with NO ₃ ^- . Steadystate NO ₃ ^- uptake was less affected by NO ₂ ^- than was steady-state NO ₂ ^- uptake by NO ₃ ^- . Nitrate reductase activity (NRA) in leaves and roots was induced by both NO ₃ ^- and NO ₂ ^- . In roots, induction with NO ₂ ^- was faster than with NO ₃ ^- , but there was no difference in NRA after 5 h. Nitrite inhibited NRA in the roots of NO ₃ ^- -induced plants and thus seems to stimulate the induction, but not the activity of induced nitrate reductase. In view of the observed differences in time course and mutual competition, a common uptake mechanism for NO ₂ ^- and NO ₃ ^- seems unlikely. Expression of the NO ₂ ^- effect on the induction of NO ₃ ^- uptake required more time than the induction itself. We therefore conclude that NO ₂ ^- is not the physiological inducer of NO ₃ ^- uptake.Abbreviations NR(A) nitrate reductase (activity) - BM basal medium     

Au(III)-complexes of the alanyl-containing peptides glycylalanine and glycylalanylalanine - Synthesis, spectroscopic and structural characterization

As part of an investigation on the coordination ability of peptides, the dipeptide glycylalanine (H-Gly-Ala-OH), tripeptide glycylalanylalanine (H-Gly-Ala-Ala-OH) and their Au(III)-complexes have been characterized structurally. The quantum chemical calculations and linear-dichroic infrared (IR-LD) spectroscopy predict structures of the compound studied, which are compared with a single crystal X-ray diffraction of H-Gly-Ala-OH. The coordination processes with Au(III) are supported by data for ¹H NMR, ESI-MS, HPLC-MS-MS, TGV and DSC methods. The [Au(Gly-Ala)H₋₁Cl] and [Au(Gly-Ala-Ala)H₋₂] · 2H₂O complexes are formed via -NH₂, N⁻amide/s and groups of the peptides. One Cl⁻ ion is attached to the metal center as terminal ligand in the first complex. In both cases a near to square-planar geometry of the chromophors AuN₂OCl and AuN₃O is yielded.     

Expression of Na+/HCO3- cotransporter and its role in pH regulation in mouse parotid acinar cells

Ion transporters such as Na(+)/H(+) exchanger (NHE), Cl(-)/HCO(3)(-) exchanger (AE), and Na(+)/HCO(3)(-) cotransporter (NBC) are known to contribute to the intracellular pH (pH(i)) regulation during agonist-induced stimulation. This study examined the mechanisms for the pH(i) regulation in the mouse parotid and sublingual acinar cells using the fluorescent pH-sensitive probe, BCECF. The pH(i) recovery from agonist-induced acidification in the sublingual acinar cells was completely blocked by EIPA, a NHE inhibitor. However, the parotid acinar cells required DIDS, a NBC1 inhibitor, in addition to EIPA in order to block the pH(i) recovery. Moreover, RT-PCR analysis detected the expression of pancreatic NBC1 (pNBC1) only in the parotid acinar cells. These results provide strong evidence that the mechanisms for the pH(i) regulation are different in the two types of acinar cells, and pNBC1 contributes to pH(i) regulation in the parotid acinar cells, whereas NHE is likely to be the exclusive pH(i) regulator in the sublingual acinar cells.     

辽东山区次生林生态系统不同林型树干茎流的理化性质

为明确森林对降雨水质的影响,于2011年6-8月,对辽东山区次生林生态系统5种主要林型:落叶松人工林(Larix olgensis)(Lo)、花曲柳林(Fraxinus rhynchophulla)(Fr)、杂木林(Mb)、红松人工林(Pinus koraiensis(Pk)和蒙古栎林(Querus mongolica)(Om)中树干茎流和林外雨理化性质进行了监测.与林外雨相比,5种林型树干茎流均出现明显酸化(P＜0.05),酸化程度为:Pk＞ Lo＞ Fr＞ Om＞ Mb;各林型树干茎流的电导率、总溶解固体含量、氯离子浓度、硝酸根离子浓度、铵根离子浓度浓度和总磷浓度显著升高(P＜0.05),溶解氧浓度明显下降(P＜0.05).林型间相比,Lo与Pk的电导率和总溶解固体含量和Lo的氯离子浓度较高;Lo和Pk的硝酸根离子浓度和总磷浓度明显低于其它林型(P＜0.05);Mb的硝酸根离子浓度和总磷浓度显著高于其它林型(P＜0.05).各林型树干茎流的硝酸根离子浓度和胸径与树高的乘积呈显著正相关.上述结果主要受降雨因素(降雨前干沉降时间长度等)、林分特征(叶面积指数、树皮特征)、树木枝叶表层积累物质的理化性质等影响.结论:各林型树干茎流水质均明显下降,其中Mb树干茎流对雨水化学性质影响较大;Pk和Lo树干茎流水体纯度下降最为显著.     

HCO 3 - and OH-transport across the plasmalemma ofChara

Internodal and whorl (branch) cells of the green alga,Chara corallina Klein ex Willd., em. R.D.W., were studied with the extracellular vibrating probe for measuring transmembrane ion currents, and with an extracellular pH microprobe for measuring the surface pH profile. Bands of positive inward current (OH^- efflux) 1–3 mm wide were separated by wider bands of outward current (HCO ₃ ^- influx) along the length of the cell. The measured peaks of inward current ranged from 20 to 60 A cm^-2 (98 m from the cell surface) which would correspond to a surface ionic flux of 270–800 pmol cm^-2 s^-1. The peaks of outward current (HCO ₃ ^- influx) ranged from 10 to 30 A cm^-2 which would correspond to a surface ionic flux of 140–400 pmol cm^-2 s^-1. The inward current bands matched the regions of surface alkalinity very well. The outward current (HCO ₃ ^- influx) was reduced at least 10-fold in low-HCO ₃ ^- medium, with a commensurate readjustment in the strength and pattern of inward current (OH^- efflux). (Although these experiments involved a manipulation of the external pH, it is felt that the main adjustment in current patterns was in response to the reduction in exogenous HCO ₃ ^- ). The presence of the vibrating probe perturbed the inward current region when vibrating with a 26-m amplitude, but this perturbation was eliminated when a 7-m amplitude was used. The perturbation was usually observed as a reduction in the number of inward current peaks with an increase (approximate doubling) in the amplitudes of the one or two remaining peaks. Both the inward and outward currents were light-dependent, falling off within seconds of light removal.     

X-ray diffraction and high-resolution NMR spectroscopy of methyl 3-azido-2,3-dideoxy-alpha-D-lyxo-hexopyranoside

The single-crystal X-ray diffraction and high-resolution 1H and 13C NMR spectral data for the title compound are reported. The influence of the ring oxygen atom on the J(1,2e) and J(4,5) coupling constants for 2-deoxy-D-lyxo- and -D-xylo-hexopyranosides is discussed.     

On the metabolic activation of the carcinogen N-hydroxy-N-2-acetylaminofluorene : III. Oxidation with horseradish peroxidase to yield 2-nitrosofluorene and N-acetoxy-N-2-acetylaminofluorene

Previous studies have shown that the carcinogen N-hydroxy-2-acetylaminofluorene is converted by one-electron oxidants to a free nitroxide radical which dismutates to N-acetoxy-2-acetylaminofluorene and 2-nitrosofluorene. The present study shows that the same oxidation can be achieved with horseradish peroxidase and H₂O₂. The free radical intermediate was detected by its ESR signal, and the yields of N-acetoxy-2-acetylaminofluorene and of 2-nitrosofluorene were determined under a number of conditions. Addition of tRNA to the reaction mixture containing N-acetoxy-N-2-acetyl[2′-³H]aminofluorene yielded tRNA-bound radioactivity; addition of guanosine yielded a reaction product which appears to be N-guanosin-8-yl)-2-acetylaminofluorene. The latter compound has previously been identified as a reaction product of N-acetoxy-2-acetylaminofluorene and guanosine. Preliminary attempts to demonstrate the formation of a nitroxide free radical or its dismutation products with rat liver mixed function oxidase systems were not successful.