Purification and characterization of endo-xylanases from Aspergillus niger. II. An enzyme of pl 4.5

A homogeneous endo-xylanase (1,4-beta-D-xylan xylanohydrolase, EC 3.2.1.8) was obtained from a crude Aspergillus niger pentosanase by chromatography with Ultrogel AcA 54, SP-Sephadex C-25 at pH 4.5, DEAE-Sephadex A-25 at pH 5.4, Sephadex G-50, and SP-Sephadex C-25 with a gradient from pH 2.8 to pH 4.6. It was much more active on soluble than on insoluble xylan, yielding large amounts of unreacted xylan and a mixture of oligosaccharides with chain lengths from two to six. No xylose or L-arabinose was produced. There was high activity on a xylopentaose through xylononaose mixture, but not on xylobiose, xylotriose, or xylotetraose. The enzyme had slight activity on untreated cellulose, carboxymethylcellulose, and pectin. Molecular weight was ca. 1.4 x 10(4), with an isoelectric point of 4.5 and an amino acid profile high in acidic but low in sulfur-containing residues. In a 25-min assay at pH 4.7, this endo-xylanase was most active at 45 degrees C, with an activation energy from 5 to 35 degrees C of 33.3 kJ/mol. The optimum pH for activity was 4.9. Decay in buffer was first order, with an activation energy at pH 4.7 from 48 to 53 degrees C of 460 kJ/mol. Optimum pH for stability was about 5.6, where the half-life at 48 degrees C in buffer was ca. 40 h.     

Design and synthesis of conformationally constrained 3-(N-alkylamino)propylphosphonic acids as potent agonists of sphingosine-1-phosphate (S1P) receptors

A series of conformationally constrained 3-(N-alkylamino)propylphosphonic acids were systematically synthesized and their activities as S1P receptor agonists were evaluated. Several pyrrolidine and cyclohexane analogs had S1P receptor profiles comparable to the acyclic lead compound, 3-(N-tetradecylamino)propylphosphonic acid (3), lowered circulating lymphocytes in mice after iv administration and were thus identified as being suitable for further investigations.     

The discovery of 3-(N-alkyl)aminopropylphosphonic acids as potent S1P receptor agonists

3-(N-Alkyl)aminopropylphosphonic acids are potent agonists of four of the five known sphingosine-1-phosphate (S1P) receptor subtypes.     

Population dynamics ofDaphnia rosea in a small eutrophic pond

The population dynamics ofDaphnia rosea were studied in a small, eutrophic fish-free pond during November 1986–November 1987.D. rosea showed two density peaks in 1987, a high peak in spring and a slightly lower one in autumn, but they disappeared in mid- and late summer when a smaller cladoceran,Ceriodaphnia reticulata, dominated. The rapid decline in density ofD. rosea in mid-May and the low density in June/July were preceded by or coincided with a period of increased male density, the appearance of ephippial females, smaller body length of adult females, decreased brood size, and increased frequency of empty brood chambers, all of which indicate a worsening food situation. The rapid density decline ofD. rosea in mid-May was considered attributable neither to increasing water temperature, nor predation by the dipteranChaoborus flavicans, but to insufficient food conditions for the maintenance of stable reproduction. Although edible phytoplankton was abundant in June/July, the general food situation was not suitable forD. rosea due to blooms of the large-celled dinoflagellate,Ceratium hirundinella, which probably inhibited the feeding activity ofD. rosea. TheC. hirundinella blooms might also be important for the shift of the dominant herbivore from the largerD. rosea to the smallerCeriodaphnia reticulata in August/September.     

Two-dimensional NMR studies and secondary structure of cobrotoxin in aqueous solution

The 1H-NMR spectra of cobrotoxin, a neurotoxic protein isolated from Formosan cobra Naja naja atra, have been studied by two-dimensional NMR techniques. Of 62 amino acid residues in cobrotoxin, the complete assignments of 58 residues have been made. The resonances from several of the remaining residues have been identified but not yet specifically assigned. The secondary structure of an antiparallel triple- and double-stranded beta-sheet has also been determined by observing the NOE.     

Characterization of a novel sphingosine 1-phosphate receptor, Edg-8

Three G protein-coupled receptors (Edg-1, Edg-3, and Edg-5) for the lysolipid phosphoric acid mediator sphingosine 1-phosphate have been described by molecular cloning. Using a similar sequence that we found in the expressed sequence tag data base, we cloned and characterized of a fourth, high affinity, rat brain sphingosine 1-phosphate receptor, Edg-8. When HEK293T cells were co-transfected with Edg-8 and G protein DNAs, prepared membranes showed sphingosine 1- phosphate-dependent increases in [(35)S]guanosine 5'-(3-O-thio)triphosphate binding with an EC(50) of 90 nm. In a rat hepatoma Rh7777 cell line that exhibits modest endogenous responses to sphingosine 1-phosphate, this lipid mediator inhibited forskolin-driven rises in cAMP by greater than 90% when the cells were transfected with Edg-8 DNA (IC(50) 0.7 nm). This response is blocked fully by prior treatment of cultures with pertussis toxin, thus implicating signaling through G(i/o)alpha proteins. Furthermore, Xenopus oocytes exhibit a calcium response to sphingosine 1-phosphate after injection of Edg-8 mRNA, but only when oocytes are co-injected with chimeric G(q/i)alpha protein mRNA. Membranes from HEK293T and Rh7777 cell cultures expressing Edg-8 exhibited high affinity (K(D) = 2 nm) binding for radiolabeled sphingosine 1-phosphate. Rat Edg-8 RNA is expressed in spleen and throughout adult rat brain where in situ hybridization revealed it to be associated with white matter. Together our data demonstrate that Edg-8 is a high affinity sphingosine 1-phosphate receptor that couples to G(i/o)alpha proteins and is expressed predominantly by oligodendrocytes and/or fibrous astrocytes in the rat brain.     

Diversification of floral orientation in Lonicera is associated with pollinator shift and flowering phenology

Floral orientation has been suggested to be a functional floral trait that can enhance reproductive fitness through adaptation to both biotic factors (e.g., pollination) and abiotic factors (e.g., temperature). However, whether those factors drive the diversification of floral orientation needs to be explored through multiple related species. Phylogenetic relationships in Lonicera were identified by incorporating the species’ floral orientation (upward vs. downward) and pollinator types. Furthermore, transitions in floral orientation were evaluated together with pollinator shift, and seven Lonicera species were used to detect the influence of floral orientation on pollination and reproductive success. The relationship between temperature and the angle of floral orientation was investigated. Floral orientation in Lonicera showed that most of the closely related species within the same node displayed a similar pattern of floral orientation, and pollinator shift can lead to transitions between upward and downward orientation. Additionally, the angle of floral orientation increased with flowering phenology from spring to summer, and changing floral orientation significantly decreased pollination and seed production. Moreover, the average daily temperature during flowering phenology was significantly correlated with the angle of floral orientation. Our results indicate that pollinator shift could be an important event, leading to the diversification of floral orientation. Results of field investigations inferred that floral orientation should be a functional floral trait adapted to flowering phenology. Downward-facing flowers might help decrease heat loss to adapt to cold conditions. This study disentangled the influences of historical events and local adaptation on the evolution of floral orientation.     

贠建全:广东荷包岛维管束植物名录

以分布于秦岭的金花忍冬（Lonicera chrysantha Turcz.）、忍冬（L.japonica Thunb.）、葱皮忍冬（L.ferdinandii Franch.）和金银忍冬（L.maackii（Rupr.）Maxim.）为对象,通过定位观察、人工授粉实验、人为设置实验斑块的方法对忍冬属4种植物的开花生物学特性、繁育系统、花色变化现象、传粉过程进行了研究。结果表明,4种植物的单花花期、花部特征存在差异。人工授粉实验显示,4种植物均存在一定的花粉限制,自交不亲和。除葱皮忍冬外,其余3种植物随着花色由白变黄,花粉和花蜜报酬减少、雌雄生殖能力逐渐降低;葱皮忍冬花变色后花蜜量变化不显著,且仍保留较强的雌性生殖能力。变色花的保留被认为是植物的一种生殖策略,通过增大植物的花展示来扩大自身的吸引力,以吸引更多远距传粉者访花。人为控制白、黄花不同数量比的实验结果表明,大多数传粉者偏向访问白花（变色前的花）,且白花提供的报酬量和黄花（变色后的花）数量显著影响传粉者的访花频率,即当花蜜量减少或黄花数量增多时,传粉者访花频率随之降低。因此,我们认为忍冬属4种植物的花色变化可能除了增大植物对远距传粉者的吸引力外,对近距传粉者的访花行为也可能具有一定的影响。当传粉者接近植株时,变色后的花可能暗示其花蜜（花粉）报酬已经发生变化,并驱使昆虫离开并飞向同株或异株植物新开放的报酬丰富的白花,这既有利于提高传粉者的觅食效率,又能降低植物同株异花授粉的几率,对忍冬属植物及传粉者都具有重要意义,是植物长期与授粉昆虫相互适应的反映。     

Discovery of 3-arylpropionic acids as potent agonists of sphingosine-1-phosphate receptor-1 (S1P1) with high selectivity against all other known S1P receptor subtypes

A series of 3-arylpropionic acids were synthesized as S1P1 receptor agonists. Structure-activity relationship studies on the pendant phenyl ring revealed several structural features offering selectivity of S1P1 binding against S1P2-5. These highly selective S1P1 agonists induced peripheral blood lymphocyte lowering in mice and one of them was found to be efficacious in a rat skin transplantation model, supporting that S1P1 agonism is primarily responsible for the immunosuppressive efficacy observed in preclinical animal models.