血管内皮舒张因子在氧自由基所致慢性缺氧大鼠肺内动脉收缩中的作用

以黄嘌岭(X)-黄嘌呤氧化酶(XO)系统产生氧自由基,应用微量生物测定法观察慢性缺氧(5000m,10d)对大鼠氧自由基所致肺内动脉收缩的影响及内皮舒张因子(EDRF)在其中的作用。慢性缺氧大鼠有内皮的肺内动脉环对氧自由基的收缩反应较正常环境中的对照动物明显增强,加入EDRF灭活剂还原型血红蛋白(RHb)后更加显著;而加入超氧化物歧化酶(铜锌SOD)后则减弱,甚至消除。反之,不论加入RHb或SOD对氧自由基所致去内皮肺内动脉环的收缩反应均无明显影响。上述结果表明慢性缺氧引起肺内动脉收缩增强与EDRF有密切关系:慢性缺氧可能使EDRF的作用减弱,肺内动脉对氧自由基的反应性增强。表示EDRF及其与氧自由基的关系在慢性缺氧性肺动脉高压的形成中可能具有十分重要的意义。     

三苯基锡,二环己基碳二亚胺和寡霉素对叶绿体CF0与CF1功能联系的影响

作用于H~ —ATP酶复合体质子通道的能量传递抑制剂 TPT、DQCD和 OM能明显抑制叶绿体光合磷酸化反应和膜上 ATP酶活性,减小恒态ΛpH值,加速ΛpH和515 nm吸收衰减。这种在正常叶绿体加速H_(in)~ 经CF_0外流与在残缺膜中阻塞质子外流不一致。TPT等物质是干扰了CF_0与CF_1的构象连接,使 CF_0的质子传导失去CF_1的控制,H_(in)~ 无效漏失或质子逆向转移受影响,从而抑制与质子传导紧密相关的光合磷酸化反应和膜上ATP酶活性。     

Mallomonas palaestrica sp. nov. (Synurophyceae), a new member of sect. Torquatae from Denmark

Mallomonas paluestrica sp. nov., a new member of sect. Torquatae ser. Pumilae , was found in a small Danish pond and is described and illustrated with TEM and SEM micrographs.     

Iron-bound phosphorus in marine sediments as measured by bicarbonate-dithionite extraction

A sequential five-step extraction scheme for phosphorus pools in freshwater sediment was modified for use in marine sediments. In the second step phosphate bound to reducible forms of iron and manganese (iron-bound P) is extracted by a bicarbonate buffered dithionite solution (BD-reagent). The extraction scheme was tested on sediment from 16 m water depth in Aarhus Bay, DK and used in two other marine sediments: Kattegat at 56 m and Skagerrak at 695 m depth. By comparing the BD-extractable P-pool with both the pool of iron in the BD-fraction and the pool of oxidized, amorphous or poorly crystalline iron (am.FeOOH), highly significant correlations (p < 0.001) were observed in all three sediments. Thus, we conclude that the BD-reagent was very specific for iron-bound P. Further evidence for this came from two experiments: 1) Enhanced BD treatment did not result in additional phosphate extraction and 2) by sequential extraction of phosphorus pools in pure cultures of diatoms and cyanobacteria no phosphate was recovered in the BD-fraction. The pool of am.FeOOH was very important for controlling porewater phosphate concentration which was inferred from the significant inverse relationships between the two parameters (p < 0.001) in all sediments studied. Further, an isotopic exchange experiment with ³²PO_f4/^p3– revealed that BD-extractable P was by far the most exchangeable P-pool even deep in the sediment where the pool size was small. Iron-bound P made up 33–45% of total P in the surface sediments. The ratio between iron-bound phosphate and am.FeOOH was 8–11 in Aarhus Bay and Kattegat. In Skagerrak the ratio was 17, which may indicate that the iron mineral extracted from this sediment is less capable of adsorbing phosphate or less saturated with phosphate.     

BPTI and N-terminal extended analogues generated by factor Xa cleavage and cathepsin C trimming of a fusion protein expressed in Escherichia coli

A recombinant gene for BPTI (bovine pancreatic trypsin inhibitor) is expressed in Escherichia coli using a MBP (maltose-binding protein) fusion vector. BPTI is fused through an FXa (blood coagulation factor Xa protease) target sequence (Ile-Glu-Gly-Arg) to the C-terminus of MBP. The MBP moiety of the hybrid protein enables purification in one step utilizing MBP's affinity to cross-linked amylose, and the FXa target sequence allows specific cleavage of the hybrid protein. Effective FXa cleavage is achieved by spacing the FXa target sequence and Arg-1 of the BPTI sequence with four residues (Met-Glu-Ala-Glu). The resulting N-terminal extended BPTI is readily converted to the wild-type sequence by trimming with cathepsin C exopeptidase, for the activity of which the spacing tetrapeptide is optimized. FXa cleavage is prohibited when the target sequence is placed next to Arg-1. In this construction, off-target cleavage at a somewhat homologous sequence (Val-Pro-Gly-Arg) results in five- or six-residue extended BPTI, indicating new details of the FXa specificity. The yield of highly purified recombinant BPTI is 3-6 mg/liter of culture, making the MBP-BPTI expression system convenient for the production of sufficient amounts of protein for NMR studies. 1H NMR is used to analyze the N-extended BPTI analogues.     

A PHAGOTROPHICALLY DERIVABLE GROWTH FACTOR IN THE PLASTIDIC DINOFLAGELLATE GYRODINIUM RESPLENDENS (DINOPHYCEAE)

The marine dinoflagellate Gyrodinium resplendens Hulburt is a mixotroph. It possesses chloroplasts and is photosynthetic, and it also feeds phagotrophically on another dinoflagellate, Prorocentrum minimum (Pavillard) Schiller. The species could be cultivated only in food-replete cultures. When kept in cultures without food, cellular chl a content and photosynthetic activity of G. resplendens decreased and growth ceased after a few days. In food-replete cultures, G. resplendens could grow strictly heterotrophically in darkness, but growth rate was then three times lower than in food-replete cultures kept in light. It is suggested that the main importance of phagotrophy is to acquire a growth factor essential to photosynthetic growth. The addition of soil extract or amino acids to the growth medium induced enhanced photosynthetic growth of the species even without the presence of particulate food, but only for approximately 2 weeks. Long-term starvation of G. resplendens led to loss of the ability to feed, and therefore starved cells eventually reached a point of no return where neither photosynthesis nor phagotrophy could sustain further growth. Light microscopical observations on G. resplendens revealed new morphological and behavioral details of the species.     

Two types of cold sensitivity associated with the A184-->V change in the DnaA protein

Multicopy dnaA(Ts) strains carrying the dnaA5 or dnaA46 allele are high-temperature resistant but are cold sensitive for colony formation. The DnaA5 and DnaA46 proteins both have an A184-->V change in the ATP binding motif of the protein, but they also have one additional mutation. The mutations were separated, and it was found that a plasmid carrying exclusively the A184-->V mutation conferred a phenotype virtually identical to that of the dnaA5 plasmid. Strains carrying plasmids with either of the additional mutations behaved like a strain carrying the dnaA+ plasmid. In temperature downshifts from 42 degrees C to 30 degrees C, chromosome replication was stimulated in the multicopy dnaA46 strain. The DNA per mass ratio increased threefold, and exponential growth was maintained for more than four mass doublings. Strains carrying plasmids with the dnaA(A184-->V) or the dnaA5 gene behaved differently. The temperature downshift resulted in run out of DNA synthesis and the strains eventually ceased growth. The arrest of DNA synthesis was not due to the inability to initiate chromosome replication because marker frequency analysis showed high initiation activity after temperature downshift. However, the marker frequencies indicated that most, if not all, of the newly initiated replication forks were stalled soon after the onset of chromosome replication. Thus, it appears that the multicopy dnaA(A184-->V) strains are cold sensitive because of an inability to elongate replication at low temperature. The multicopy dnaA46 strains, on the contrary, exhibit productive initiation and normal fork movement. In this case, the cold-sensitive phenotype may be due to DNA overproduction.     

Enzymatic hydrolysis and fermentation of palm kernel press cake for production of bioethanol

Palm kernel press cake (PKC) is a residue of palm oil extraction, which was found to contain 48.5% of total carbohydrates of which 35.2% was mannan. The present study examines enzymatic hydrolysis of polysaccharides from the cell-wall material present in PKC to obtain monosaccharides that can be substrate in various fermentation processes such as ethanol production. The requirements for pretreatment were investigated and it was found that mannan in PKC was readily hydrolysed without any pretreatment. Several enzyme preparations were tested and Mannaway 25L was found as the best for releasing mannose, and Gammanase 1.0L worked well in degrading cellulose and mannose. Binary mixtures of enzymes were tested to increase the conversion, and 1:1 mixture of Mannaway 25L and Gammanase 1.0L showed good synergistic effect releasing 30% more mannose than the sum obtained using these enzymes individually. Using an enzyme loading of 2.3 mg protein/g PKC resulted in 63% of mannan in PKC being hydrolysed to mannose in 24 h, and in 96 h a total of 365 g mannose and glucose could be produced per kg PKC. Finally, PKC was hydrolysed and fermented using Saccharomyces cerevisiae with an ethanol yield of 125 g/kg PKC.