Crystals of haemoglobin with the T quaternary structure bind oxygen noncooperatively with no Bohr effect

The relationship between the structure and function of haemoglobin has mainly been studied by comparing its X-ray crystal structures with its function in solutions. To make a direct comparison we have studied the functional properties of haemoglobin in single crystals, an approach that has been an important part of the investigation of several enzyme mechanisms. Here we report on the oxygen binding by single crystals of human haemoglobin grown in solutions of polyethylene glycol. Unlike haemoglobin crystals formed in concentrated salt solution, which crack and become disordered on oxygenation, crystals grown in polyethylene glycol remain intact. X-ray studies have shown that the T (deoxy) quaternary structure of haemoglobin in this crystal at pH 7.0 is maintained at atmospheric oxygen pressure, and that the salt-bridges are not broken. We find striking differences between oxygen binding by haemoglobin in this crystal and by haemoglobin in solution. Not only is oxygenation of the crystal noncooperative, but the oxygen affinity is independent of pH in the range 6.0-8.5, and is much lower than that of the T state in solution. The lack of cooperativity without a change in quaternary structure is predicted by the two-state allosteric model of Monod, Wyman and Changeux. The absence of a Bohr effect without breakage of salt-bridges is predicted by Perutz's stereochemical mechanism. In contrast to the X-ray result that oxygen binds only to the alpha haems, our measurements show that the alpha haems have only a slightly higher affinity than the beta haems.     

3种杀虫剂对杨树羧酸酯酶的抑制效果

研究了酶浓度、底物浓度、反应体系pH、反应温度、反应时间5个因素对美洲黑杨羧酸酯酶(CarE)活性测定的影响,得出测定杨树CarE的最适反应条件为:酶稀释10倍,底物浓度为3×10-4mol/L,pH为7.0,温度30℃,时间15 min。利用试验得到的反应最适条件分析了氧化乐果、吡虫啉和氟虫腈3种内吸性药剂对杨树CarE活性的影响。结果表明:400、1 600、3 200和6 400mg/L氧化乐果能明显抑制杨树CarE活性,其中6 400 mg/L氧化乐果抑制作用最强。50、100、200、400和800 mg/L吡虫啉处理杨树48 h,对杨树CarE均没有显著影响;当处理96 h时,400和800 mg/L吡虫啉能显著抑制CarE活性。而400 mg/L氟虫腈处理杨树48 h,800 mg/L氟虫腈处理杨树96 h,都能显著抑制杨树CarE活性。     

梯级生态浮床系统处理黑臭河水除磷性能研究

以上海市某黑臭河道为处理对象,通过模拟天然水体中水生植物的分布,构建逐级下沉式梯级浮床系统(Staged Floating Treatment Wetlands,SFTWs),分析温度、植物种类、pH值和溶解氧(DO)等因素对浮床系统的除磷性能的影响.结果表明,浮床系统的除磷率受温度变化较为明显,一定温度范围内两者呈正...     

Primary sequence of a dimeric bacterial haemoglobin from Vitreoscilla

Vitreoscilla, a filamentous bacterium in the Beggiatoa family, synthesizes a soluble haem-protein which has two identical subunits of relative molecular mass 15,775 and two b haems per molecule. It is synthesized in relatively large quantities when the organism, a strict aerobe, is grown under hypoxic conditions. It forms a relatively stable oxygenated form which is spectrally similar to oxymyoglobin (oxyHb) and oxyhaemoglobin (oxyHb). The amino acid sequence of this protein has been determined and aligned to fit the helical regions of several animal and plant globins. This alignment is consistent with its being a structural homologue of the eucaryotic haemoglobins although it diverged from the others in the N-terminal region and may lack an A-helix. It showed the maximum sequence homology (24%) with lupin leghaemoglobin (Lb). Vitreoscilla Hb is the first bacterial haemoglobin to be sequenced. It may function to enable the organism to survive in oxygen-limited environments by acting as an oxygen storage-trap or to facilitate oxygen diffusion.     

浓盐水制备高纯氢氧化镁过程中钙杂质的去除研究

采用碳酸钠法,对海水淡化后产生的浓盐水制备高纯氢氧化镁过程中的钙杂质去除进行实验研究,并确定去除的最佳工艺条件.结果表明,4种影响因素对Ca2＋去除率影响顺序为：反应时间〉原料卤水的浓度〉反应温度〉Na2CO3与Ca2＋的物质的量之比;对Mg2＋去除率的影响顺序为：原料卤水的浓度〉反应时间〉反应温度〉Na2CO3与Ca2＋的物质的量之比.Ca2＋去除的最佳工艺条件为：相对密度为1.066 5的浓盐水,加入的Na2CO3与Ca2＋物质的量之比为1∶1,反应温度50℃,反应时间30 min.在最佳工艺条件下,Ca2＋去除率为80%左右,Mg2＋去除率为20%左右.     

Vision. Realignment of cones after cataract removal

Through unique observations of an adult case of bilateral congenital cataract removal, we have found evidence that retinal photoreceptors will swiftly realign towards the brightest regions in the pupils of the eye. Cones may be phototropic, actively orientating themselves towards light like sunflowers in a field.     

铁矾渣微波硫酸化焙烧水浸液的深度除铁

采用微波低温硫酸化焙烧-水浸和针铁矿除铁方法将Zn、Cu等富集到浸出液中,Pb和Ag富集到浸出渣中,使有价金属得到清洁的回收利用.研究了上述工艺中浸出液除铁的优化工艺条件,探究了反应体系的pH值、浸出液单次滴加量、浸出液的铁含量等因素对除铁效果的影响,并采用X射线衍射分析、扫描电子显微镜观察等手段对得到的沉淀渣进行了表征.研究获得的优化实验条件为：以200 mL的0.01 mol·L-1 ZnSO4溶液为底液,晶种添加量为20 g·L-1,除铁体系pH值控制在3左右,温度90℃,每隔5 min滴加3 mL水浸液(保持反应体系中铁的浓度<1 g·L-1).在此条件下,除铁后溶液残铁量仅为0.065 g·L-1,去除率可达99.3%,达到了深度除铁效果.除铁过程中,Zn的损失率仅为4.1%.