Na+-dependent alkaline earth metal uptake in cardiac sarcolemmal vesicles

The ability of alkaline earth metals (M2+) to substitute for Ca2+ in Na+-Ca2+ exchange was examined in sarcolemmal vesicles isolated from the canine heart. 85Sr2+ and 133Ba2+, in addition to 45Ca2+, were used to determine the characteristics of Na+-M2+ exchange. The Na+i-dependent M2+ uptake was measured as a function of time, with t ranging from 0.5 to 360 s, [Na+]i = 140 mM and [M2+]o = 40 microM. This function was linear for Ca2+ and Sr2+ uptake for approx. 6 s and for Ba2+ for about 60 s. Plateau levels were achieved within 120 s for Ca2+ and Sr2+ but Ba2+ took considerably longer. The Km values for Na+-M2+ exchange, derived from Eadie-Hofstee plots, were 30, 58, and 73 microM for Ca2+, Sr2+ and Ba2+, respectively. The Na+i-dependent uptake of all three ions was stimulated in the presence of 0.36 microM valinomycin. Na+-Ca2+ exchange was also measured in the presence of either 20 microM Sr2+ or 100 microM Ba2+. Both of these ions behaved (at these concentrations) as competitive inhibitors of Na+-Ca2+ exchange with the KI being 32 microM for Sr2+ and 92 microM for Ba2+. Passive efflux was determined by first allowing Na+-M2+ exchange to continue to plateau values and then diluting the loaded vesicles in the presence of EGTA. The rate constants for the passive efflux were 8.4, 6.3 and 4.4 min-1 for Ca2+, Sr2+ and Ba2+, respectively.     

兜兰亚属12种植物的核型分析

对兜兰亚属(Paphiopedilum subgenus Paphiopedilum)12种植物的染色体数目和核型进行了研究。结果表明：这12种植物的染色体数目和核型存在差异,其中菲律宾兜兰(P. philippinense)的核型公式为2n=2x=26=16m+10sm, 长瓣兜兰(P. dithanum)为2n=2x=26=20m+6sm, 密毛兜兰(P. densissimum)为2n=2x=26=22m+4sm, 飘带兜兰(P. parishii)和带叶兜兰(P. hirsutissimum)为2n=2x=26=24m+2sm, 亨利兜兰(P. henryanum)、虎斑兜兰(P. markianum)和根茎兜兰(P. rhizomatosum)为2n=2x=26=26m, 而胼胝兜兰(P. callosum)为2n=2x=32=2M+24m+6sm, 布玲兜兰(P. microchilum)为2n=2x=38=28m+10sm, 卷萼兜兰(P. appletonianum)和海南兜兰(P. hainanensis)为2n=2x=38=30m+8sm。兜兰亚属的染色体主要为中部着丝粒染色体, 未见随体;最长染色体与最短染色体之比为2.07~3.44, 臂比大于2的染色体比率为0~0.231,核不对称系数为53.50%~58.95%。长瓣兜兰、飘带兜兰、亨利兜兰、密毛兜兰、虎斑兜兰、带叶兜兰和根茎兜兰等6种的核型类型为1B型,其余6种为2B型。     

我国部分热带果树染色体研究

本试验所用材料采自华南植物园,广东省农科院果树所和云南西双版纳热带植物所。凭证标本保存在南开大学生物系标本室。春季当幼芽萌发时采取幼芽或幼叶用去壁低渗法进行染色体标本制片。按第一届全国植物染色体学术讨论会的规定进行染色体分析。     

Direct measurements of steady-state kinetics of cyanobacterial n(2) uptake by membrane-leak mass spectrometry and comparisons between nitrogen fixation and acetylene reduction

A mass spectrometer with a membrane-covered inlet was used to measure nitrogen fixation by following changes in the concentration of dissolved N(2) in a stirred suspension of the cyanobacterium Anabaena variabilis in an open system. The results showed a good fit to Michaelis-Menten kinetics with a K(m) for N(2) of 65 muM at 35 degrees C, corresponding to 0.121 atmosphere of N(2). Corresponding values for the K(m) for acetylene reduction were 385 muM (0.011 atmosphere at 35 degrees C). Comparison of the values of V(max) for N(2) uptake with those for the acetylene reduction assay under similar conditions gave an average value of 3.8 for the conversion factor between N(2) and C(2)H(2) reduction. Reduction of protons to hydrogen was completely inhibited at sufficiently high concentrations of C(2)H(2), but even at saturating N(2) concentrations, 1 mol of H(2) was produced for every mole of N(2) reduced. This explains the finding that the observed C(2)H(2)/N(2) ratio is higher than the value of 3 expected from the requirement for two electrons for acetylene reduction and six for nitrogen reduction. The results correlate well with a mechanism for N(2) reduction involving the equation: N(2) + 8H + 8e --> 2NH(3) + H(2) which gives a conversion factor between C(2)H(2) and N(2) of 4. It is proposed that, in general, 4 is a more appropriate value than 3 for the conversion factor.     

Interaction of Drosophila melanogaster prohormone convertase 2 and 7B2. Insect cell-specific processing and secretion

The prohormone convertases (PCs) are an evolutionarily ancient group of proteases required for the maturation of neuropeptide and peptide hormone precursors. In Drosophila melanogaster, the homolog of prohormone convertase 2, dPC2 (amontillado), is required for normal hatching behavior, and immunoblotting data indicate that flies express 80- and 75-kDa forms of this protein. Because mouse PC2 (mPC2) requires 7B2, a helper protein for productive maturation, we searched the fly data base for the 7B2 signature motif PPNPCP and identified an expressed sequence tag clone encoding the entire open reading frame for this protein. dPC2 and d7B2 cDNAs were subcloned into expression vectors for transfection into HEK-293 cells; mPC2 and rat 7B2 were used as controls. Although active mPC2 was detected in medium in the presence of either d7B2 or r7B2, dPC2 showed no proteolytic activity upon coexpression of either d7B2 or r7B2. Labeling experiments showed that dPC2 was synthesized but not secreted from HEK-293 cells. However, when dPC2 and either d7B2 or r7B2 were coexpressed in Drosophila S2 cells, abundant immunoreactive dPC2 was secreted into the medium, coincident with the appearance of PC2 activity. Expression and secretion of dPC2 enzyme activity thus appears to require insect cell-specific posttranslational processing events. The significant differences in the cell biology of the insect and mammalian enzymes, with 7B2 absolutely required for secretion of dPC2 and zymogen conversion occurring intracellularly in the case of dPC2 but not mPC2, support the idea that the Drosophila enzyme has specific requirements for maturation and secretion that can be met only in insect cells.     

7种橐吾属植物的核型

研究了7种橐吾属（Ligularia）植物的染色体和核形态。干崖子橐吾（L．kanaitzensis）的核型为2n＝2x＝58＝26m＋28sm 4st;窄头橐吾（L.stenocephala）的核型为2n=2x=58=26m 32sm;细茎橐吾（L.hookeri）的核型为2n=2x=58=30m 26sm 2st;宽戟橐吾（Llatihastata）的核型为2n=2x=58=28m 26sm(2sat) 4st;网脉橐吾（L.dictyoneura）的核型为2n=2x=58=26m 28sm 2st 2t;蹄橐吾（L.hodgsonii）的核型为2n=2x=58=28m 28sm 2t;棉毛橐吾（L.vellerea）的核型为2n=2x=58=22cm 34sm 2t。虽然这7个种的染色体数目相同,2n=58,核型主要是由m和sm染色体构成,但各类的染色体数目在种间有差异。核的对称性高,着丝点端值（T．C）为61．45％－64．96％。除窄头橐吾和鹿蹄橐吾的染色体数与前人报道的相同外,其它5个种的染色体数目和核型为首次报道。     

Swc2 is a widely conserved H2AZ-binding module essential for ATP-dependent histone exchange

The histone variant H2AZ is incorporated preferentially at specific locations in chromatin to modulate chromosome functions. In Saccharomyces cerevisiae, deposition of histone H2AZ is mediated by the multiprotein SWR1 complex, which catalyzes ATP-dependent exchange of nucleosomal histone H2A for H2AZ. Here, we define interactions between SWR1 components and H2AZ, revealing a link between the ATPase domain of Swr1 and three subunits required for the binding of H2AZ. We discovered that Swc2 binds directly to and is essential for transfer of H2AZ. Swc6 and Arp6 are necessary for the association of Swc2 and for nucleosome binding, whereas other subunits, Swc5 and Yaf9, are required for H2AZ transfer but neither H2AZ nor nucleosome binding. Finally, the C-terminal alpha-helix of H2AZ is crucial for its recognition by SWR1. These findings provide insight on the initial events of histone exchange.     

Activation by divalent cations of a Ca2+-activated K+ channel from skeletal muscle membrane

Several divalent cations were studied as agonists of a Ca2+-activated K+ channel obtained from rat muscle membranes and incorporated into planar lipid bilayers. The effect of these agonists on single-channel currents was tested in the absence and in the presence of Ca2+. Among the divalent cations that activate the channel, Ca2+ is the most effective, followed by Cd2+, Sr2+, Mn2+, Fe2+, and Co2+. Mg2+, Ni2+, Ba2+, Cu2+, Zn2+, Hg2+, and Sn2+ are ineffective. The voltage dependence of channel activation is the same for all the divalent cations. The time-averaged probability of the open state is a sigmoidal function of the divalent cation concentration. The sigmoidal curves are described by a dissociation constant K and a Hill coefficient N. The values of these parameters, measured at 80 mV are: N = 2.1, K = 4 X 10(-7) mMN for Ca2+; N = 3.0, K = 0.02 mMN for Cd2+; N = 1.45, K = 0.63 mMN for Sr2+; N = 1.7, K = 0.94 mMN for Mn2+; N = 1.1, K = 3.0 mMN for Fe2+; and N = 1.1 K = 4.35 mMN for Co2+. In the presence of Ca2+, the divalent cations Cd2+, Co2+, Mn2+, Ni2+, and Mg2+ are able to increase the apparent affinity of the channel for Ca2+ and they increase the Hill coefficient in a concentration-dependent fashion. These divalent cations are only effective when added to the cytoplasmic side of the channel. We suggest that these divalent cations can bind to the channel, unmasking new Ca2+ sites.     

Grb2 SH2 domain-binding peptide analogs as potential anticancer agents

The growth factor receptor-bound protein 2 (Grb2) plays an important role in the Ras signaling pathway. Several proteins were found to be overexpressed by oncogenes in the Ras signaling pathway, rendering Grb2 a potential target for the design of antitumor agents. Blocking the interaction between the phosphotyrosine-containing activated receptor and the Src-homology 2 (SH2) domain of Grb2 thus constitutes an important strategy for the development of potential anticancer agents. X-ray, NMR structural investigations, and molecular modeling studies have provided the target structure of Grb2 SH2 domain-alone or complexed with a phosphotyrosine-containing peptide-which is useful for the structure-based design of peptides or peptidomimetics with high affinity for the Grb2 SH2 domain. We review here the variety of approaches to Grb2 SH2 pepide inhibitors developed with the aim of interrupting Grb2 recognition. Inhibitory effects of peptide analogs on the Grb2 SH2 domain and their binding affinities for Grb2 SH2 were determined by ELISA, cell-based assays, or Surface Plasman Resonance (SPR) technology. Results of theses studies provide important information for further modifications of lead peptides, and should lead to the discovery of potent peptides as anticancer agents.     

Scaffolding adapter Grb2-associated binder 2 requires Syk to transmit signals from FcepsilonRI

Scaffolding adapter Grb2-associated binder 2 (Gab2) is a key component of FcepsilonRI signaling in mast cells, required for the activation of PI3K. To understand how Gab2 is activated in FcepsilonRI signaling, we asked which protein tyrosine kinase is required for Gab2 phosphorylation. We found that Gab2 tyrosyl phosphorylation requires Lyn and Syk. In agreement with published results, we found that Fyn also contributes to Gab2 tyrosyl phosphorylation. However, Syk activation is defective in Fyn(-/-) mast cells, suggesting that Syk is the proximal kinase responsible for Gab2 tyrosyl phosphorylation. Then, we asked which domains in Gab2 are required for Gab2 tyrosyl phosphorylation. We found that the Grb2-Src homology 3 (SH3) binding sites are required for, whereas the pleckstrin homology (PH) domain contributes to, Gab2 tyrosyl phosphorylation. Using a protein/lipid overlay assay, we determined that the Gab2 PH domain preferentially binds the PI3K lipid products, PI3, 4,5P3 and PI3, 4P2. Furthermore, the Grb2-SH3 binding sites and PH domain binding to PI3K lipid products are required for Gab2 function in FcepsilonRI-evoked degranulation and Akt activation. Our data strongly suggest a model for Gab2 action in FcepsilonRI signaling. The Grb2 SH3 binding sites play a critical role in bringing Gab2 to FcepsilonRI, whereupon Gab2 becomes tyrosyl-phosphorylated in a Syk-dependent fashion. Phosphorylated Gab2 results in recruitment and activation of PI3K, whose lipid products bind the PH domain of Gab2 and acts in positive feedback loop for sustained PI3K recruitment and phosphatidylinositol-3,4,5-trisphosphate production, required for FcepsilonRI-evoked degranulation of mast cells.     

Selective dehydrogenation (oxidation) of 3,4-dimethoxybenzyl alcohol by a non-heme iron lignin-peroxidase reaction mimic.

In pyridine, bis(2,2'-bipyridine)iron(II) (Fe(bpy)2+(2)) activates hydrogen peroxide for the efficient and selective catalytic dehydrogenation (oxidation) of veratryl alcohol (model-substrate monomer for lignin; 3,4-(MeO)2PhCH2OH). Several other complexes (FeII(OPPh3)2+(4), FeII(O2bpy)2+(2), FeII(MeCN)2+(4), FeII(PA)2, FeIIICl3) are effective catalysts for the dehydrogenation of veratryl alcohol and benzyl alcohol, but their selectivity (relative reactivity with 3,4-(MeO)2PhCH2OH vs. PhCH2OH) is less than the 6.1 ratio that is observed for the optimized FeII(bpy)2+(2)/H2O2/pyridine (py) system. The reactivities have been determined for several other methoxybenzyl alcohols that are model substrates for lignin (e.g., 4-MeOPhCH2OH and (MeO)3PhCH2OH).     

Chromosome Observations of Some Medical Plants in Xinjiang

Chromosome examination was carried out in 30 medical plant species native to Xinjiang in 14 families, ten of which are traditional medical plants of the minority nationalities in the region, the karyotype analysis was also carried out in some species. Karyotype formulae are 2n=12=10Lm+2S_st^SAT for Nigella glandulifera, 2n=16= 2m+12sm+ 2st for Trollius chinensis, 2n= 16 =8m + 8sm for Astragalus membranaceus, 2n=16=10m 6 sm for Astragalus mongholicus, 2n=16=8 m+8 sm for Catharanthus roseus. The chromosomal numbers of the others are as follows: Dianthus chinensis, 2n=30, Vaccaria pyramidata, 2n=30, Cassia occidentalis, 2n=26, Psoralea corylifolia, 2n=22, Peganum harmala, 2n=22, Acanthopanax trifolitus, 2n=46, Anethum graveolens, 2n=22, Foeniculum vulgare 2n=22, Trachyspermum ammi, 2n= 18, Agastache rugosus, 2n= 18 Dracocephalum moldavica, 2n= 10, Leonurus heterophyllus, 2n=20, Ocimum basilicum, 2n=48, schizonepeta tenuifolia, 2n=24, Atropa belladonna, 2n=60 Nicandra physaloidea, 2n=20, Solanum surattense, 2n=24, Scrophularia ningpoensis, 2n= 90, Plantago insularis, 2n =8, Gardenia jasminoides, 2n =22, Platycodon grandiflorus 2n= 18, Cichorium intybus, 2n= 18, Saussuea involucrata, 2n=32, Silybum marianum, 2n=34, Vernonia anthelmintica, 2n=20. The kar-yotypes of 8 species are reported for the first time.     

白藜芦醇减轻神经元氧化应激损伤的作用机制研究

目的:观察白藜芦醇(RSV)对过氧化氢(H2O2)所致的海马神经元HT22细胞损伤的保护作用,并探讨超氧化物歧化酶2(Mn-SOD)在其中的作用。方法:采用体外培养HT22小鼠海马神经元细胞系,H2O2作为损伤因素模拟氧化应激损伤。将细胞分为5组,分别为正常培养组(Control)、150μM H2O2损伤组(H2O2)、25μM白藜芦醇保护组(RSV+H2O2)、SOD2-si RNA干扰组(SOD2-si RNA+RSV+H2O2)和乱序RNA组(SC-si RNA+RSV+H2O2),药物暴露24 h后,应用MTT法检测HT22细胞活力、比色法检测乳酸脱氢酶(Lactate Dehydrogenase,LDH)释放量、相差显微镜观测细胞形态。结果:与对照组相比,H2O2组的活力显著下降(P0.05),LDH释放量明显增加(P0.05),细胞形态明显破坏;25μM的RSV显著恢复了HT22细胞的活力、减少了LDH释放、改善了细胞形态,而SOD2-si RNA显著逆转了RSV引起的上述保护作用,乱序RNA(SC-si RNA)未对上述保护作用产生明显影响。结论:白藜芦醇可能通过上调SOD2减轻H2O2对HT22细胞的氧化应激损伤。     

黄芪属六种植物的核型多样性

采用常规压片法,对豆科黄芪属6种植物制备染色体标本进行核型分析。结果表明:体细胞中期染色体数目分别为:沙打旺、斜茎黄芪、达乌里黄芪2n=16,均为二倍体;草木樨状黄芪2n=32,为四倍体;紫云英、鹰嘴紫云英则呈现多数目性,紫云英染色体数变动范围为55～65,64条稍多,鹰嘴紫云英染色体数变动范围51～65,62条稍多,均为混倍体。核型公式分别为:沙打旺2n=2x=16=12m+4sm;斜茎黄芪2n=2x=16=10m+6sm;达乌里黄芪2n=2x=16=16m;草木樨状黄芪2n=4x=32=32m;紫云英2n=64=62m+2sm;鹰嘴紫云英2n=62=12M+50m(2SAT)。染色体核型呈现多样性。     

国产８种蜘蛛抱属植物的核型研究

首次报道了８种蜘蛛抱属植物的核型,其中６种的染色体数目为首次报道,结果如下：峨边蜘蛛抱蛋Ａ.ebianensis,2n=2x=36=18m 2sm(2sat) 16st;盈江蜘蛛抱蛋Ａ．yingjiangensis,2n=2x=36=14m 6sm(2sat) 16st;海南蜘蛛抱蛋Ａ．hainensis,2n=2x=36=20m(2sat) 14st 2t;石山蜘蛛抱蛋Ａ.saxicola,2n=2x=36=16m 4sm(2sat) 16st;要蜘蛛抱蛋白Ａ.muricata,2n=2x=36=18m 2sm(2sat) 16st);啮边蛛抱蛋Ａ.marginella,2n=2x=38=22m 4sm(2sat) 12st;西林蜘蛛抱蛋Ａ.xillinensis,2n=4x=76=48m(4sat) 2sm 26st;十字蜘蛛抱蛋A.cruciformis,2n=4x=76=46m(4sat) 12sm 18st。核型类型都为２Ｃ型。首次在中国发现了Ａ.cruciformis和A.xilinensis的野生四倍体。根据外部形态性及已有的３８种植物的核型资料分析,认为该属染色体的原始基数可能为x=18,核型向对称性增强的方向演化,其主要表现在中部着丝粒染色体数目的增多,这种演化趋似与其花部结构的进化密切相关。     

Two modes of inhibition of the Ca2+ pump in red cells by Ca2+

Two different and independent modes of inhibition of the Ca2+ pump by Ca2+ can be detected measuring active Ca2+ extrusion from resealed ghosts of human red cells: one requires extracellular and the other requires intracellular Ca2+. Ki for inhibition by extracellular Ca2+ is about 10 mM. Extracellular Mg2+ replaces Ca2+ in inhibiting Ca2+ transport but with an apparent affinity for inhibition about 3-times less than that for Ca2+. Inhibition by external Ca2+ is not affected by Na+ or K+ at both surfaces of the cell membrane, external EGTA, internal Ca2+ or ATP. The apparent affinity for external Ca2+ progressively raises as pH increases. The effects of extracellular Ca2+ and Mg2+ are consistent with the idea that for Ca2+ pumping to proceed, external sites in the pump must be protonated and not occupied by extracellular Ca2+ or Mg2+. Inhibition by intracellular Ca2+ takes place with a Ki of about 1 mM and is independent of external Ca2+. The inhibitory effects of intracellular Ca2+ can be accounted for if Ca2+ and CaATP were competitive inhibitors of the activation of the pump by Mg2+ and MgATP, respectively.     

Hydrogenase activity in Azospirillum brasilense is inhibited by nitrite, nitric oxide, carbon monoxide, and acetylene.

Nitrite, NO, CO, and C2H2 inhibited O2-dependent H2 uptake (H3H oxidation) in denitrifying Azospirillum brasilense Sp7 grown anaerobically on N2O or NO3-. The apparent Ki values for inhibition of O2-dependent H2 uptake were 20 microM for NO2-, 0.4 microM for NO, 28 microM for CO, and 88 microM for C2H2. These inhibitors also affected methylene blue-dependent H2 uptake, presumably by acting directly on the hydrogenase. Nitrite and NO inhibited H2 uptake irreversibly, whereas inhibition due to CO was easily reversed by repeatedly evacuating and backfilling with N2. The C2H2 inhibition was not readily reversed, partly due to difficulty in removing the last traces of this gas from solution. The NO2- inhibition of malate-dependent respiration was readily reversed by repeatedly washing the cells, in contrast to the effect of NO2- on H2-dependent respiration. These results suggest that the low hydrogenase activities observed in NO3(-)-grown cultures of A. brasilense may be due to the irreversible inhibition of hydrogenase by NO2- and NO produced by NO3- reduction.     

A control system for arterial blood gases

A system was developed to control arterial O2 and CO2 partial pressure (Pao2, and Paco2) simultaneously and independently of each other. The system makes changes in inspired fractional concentration of O2 and CO2 based on values for end-tidal O2 and CO2 partial pressure. The system was applied in 23 normal subjects. In attempts to maintain a Pao2 of 90 Torr and a Paco2 of 40 Torr, arterial blood gases were 91.1 +/- 6.5 (SD) Torr for Pao2 and 41.2 +/- 3.2 Torr for Paco2. In attempts to maintain a Pao2 of 40 Torr and a Paco2 of 40 Torr, arterial blood gases were 40.4 +/- 3.9 Torr for Pao2 and 38.9 +/- 2.5 Torr for Paco2. In attempts to maintain a Pao2 of 90 Torr and a Paco2 of 55 Torr, arterial blood gases were 98.1 +/- 11.5 Torr for Pao2 and 52.8 +/- 3.4 Torr for Paco2. Coefficients of variations ranged from 7.1 to 11.7% for Pao2 and 6.4 to 7.8% for Paco2.     

木兰科3个杂交组合及其亲本的核型研究

研究了木兰科（Magaoliaceae）3个杂交组合的亲本和杂交后代的核型。结果表明,云南含笑（Michelia yunnanensis）、灰岩含笑（Michelia calcicola）及其杂交组合A的核型分别为2n=2x=38=36m＋2sm、2n=2x=38=34m＋4sm和2n=2x=38=26m＋12sm;紫花含笑（Michelia crassipes）及其与云南含笑杂交组合C的核型分别为2n=2x=38=32m＋6sm和2n=2x=38=24m＋12sm＋2st;山玉兰（Mognolia delavayi）、广玉兰（Mognolia grondiflora）及其杂交组合U的核型分别为2n=2x=38=28m＋10sm、2n=6x=114=88m＋lOsm＋16st和2n=4x=76=57m＋15sm＋4st。杂交组合的核型与理论核型存在明显的差异,可能是在杂交组合的形成过程中,来自亲本的染色体发生了结构变异。