红螺菌吸附铜的动力学与脱附研究

研究了红螺菌(Rhodospirillum)对Cu~(2 )的吸附动力学行为,在一定的条件下,吸附在45 min达到平衡,吸附平衡时最大吸附量为48.23 mg·g~(-1)。应用准一级和准二级反应动力学模型进行数据分析,结果表明菌体对Cu~(2 )的吸附符合准二级动力学模型。比较分析了多种脱附剂对菌体脱附,EDTA和柠檬酸是较有效的洗脱剂,脱附率分别为86.4％、66.9％;无机酸及无机盐对菌体的脱附效果很差,脱附率在20％左右。X-射线衍射分析表明,菌体吸附Cu~(2 )后没有形成新晶相,并且菌体部分晶相转变为非晶相。     

Virus crystallography

Virus crystallography can provide atomic resolution structures for intact isometric virus particles and components thereof. The methodology is illustrated by reference to a particularly complex example, the core of the bluetongue virus (700 Å).     

Proton channel hydration and dynamics of a bacteriorhodopsin triple mutant with an M-state-like conformation

The hydration and dynamics of purple membranes (PM) containing the bacteriorhodopsin (BR) triple mutant D96G/F171C/F219L were investigated by neutron diffraction coupled with H₂O/D₂O exchange and by energy-resolved neutron scattering. The mutant, which is active in proton transport (Tittor et al. in J. Mol. Biol. 319:555–565, 2002), has an open ground-state structure similar to that of the M intermediate in the photocycle of the wild type (wt) (Subramaniam and Henderson in Nature 406:653–657, 2000). The experiments demonstrated an increased proton channel hydration in the mutant PM compared with wt PM, in both high (86%) and low (57%) relative humidity. We suggest that this is due to the smaller side chains of the mutant residues liberating space for more water molecules in the proton channel, which would then be able to participate in the proton translocation network. PM thermal dynamics has been shown to be very sensitive to membrane hydration (Lehnert et al. in Biophys. J. 75:1945–1952, 1998). The global dynamical behaviour of the mutant PM on the 100-ps time scale, as a function of relative humidity, was found to be identical to that of the wt, showing that the open BR structure and additional water molecules in the proton channel do not provide a softer environment enabling increased flexibility.     

The Kinetics of Non-Lamellar Phase Formation in DOPE-Me: Relevance to Biomembrane Fusion

The mechanism of the lamellar/inverted cubic (Q_II) phase transition is related to that of membrane fusion in lipid systems. N-Monomethylated dioleoylphosphatidylethanolamine (DOPE-Me) exhibits this transition and is commonly used to investigate the effects of exogenous substances, such as viral fusion peptides, on the mechanism of membrane fusion. We studied DOPE-Me phase behavior as a first step in evaluating the effects of membrane-spanning peptides on inverted phase formation and membrane fusion. These measurements show that: a) the onset temperatures for Q_II and inverted hexagonal (H_II) phase formation both are temperature scan rate-dependent; b) longer pre-incubation times at low temperature and lower temperature scan rates favor formation of the Q_II phase; and c) in temperature-jump experiments between 61 and 65°C, the meta-stable H_II phase forms initially, and disappears slowly while the Q_II phase develops. These observations are rationalized in the context of a mechanism for both the lamellar/non-lamellar phase transition and the related process of membrane fusion. Current address for D.P.S.: Givaudan, Cincinnati, OH 45216 Data Deposition: Relevant transition temperatures in this paper have been deposited in the LIPIDAT ( )     

Structure and catalytic mechanism of the cytosolic D-ribulose-5-phosphate 3-epimerase from rice

Cytosolic D-ribulose-5-phosphate 3-epimerase from rice was crystallized after EDTA treatment and structurally elucidated by X-ray diffraction to 1.9A resolution. A prominent Zn(2+) site at the active center was established in a soaking experiment. The structure was compared with that of the EDTA-treated crystalline enzyme from the chloroplasts of potato plant leaves showing some structural differences, in particular the "closed" state of a strongly conserved mobile loop covering the substrate at its putative binding site. The previous proposal for the active center was confirmed and the most likely substrate binding position and conformation was derived from the locations of the bound zinc and sulfate ions and of three water molecules. Assuming that the bound zinc ion is an integral part of the enzyme, a reaction mechanism involving a well-stabilized cis-enediolate intermediate is suggested.     

Effect of calcium ions on the organization of iota-carrageenan helices: an X-ray investigation

X-ray fiber diffraction analysis confirms that calcium iota-carrageenan forms a threefold, right-handed, half-staggered, parallel, double helix of pitch 26.42 A stabilized by interchain hydrogen bonds. According to the detailed structural results, three helices are packed in a trigonal unit cell (a=23.61 and c=13.21 A). Strong interactions between the sulfate groups of neighboring helices, mediated by calcium ions and water molecules, are responsible for stabilizing the three-dimensional structure.     

Confirmation of the structure of tetra-O-(tert-butyldimethylsilyl)-D-glucono-1,4-lactone formed by silylation of D-glucono-1,5-lactone

The structure of tetra-O-(tert-butyldimethylsilyl)-D-glucono-1,4-lactone made by the silylation of D-glucono-1,5-lactone has been confirmed by single-crystal X-ray analysis.     

On the Configurational and Conformational Changes in Photoactive Yellow Protein that Leads to Signal Generation in Ectothiorhodospira halophila

Photoactive Yellow Protein (PYP), a phototaxis photoreceptor from Ectothiorhodospira halophila, is a small water-soluble protein that iscrystallisable and excellently photo-stable. It can be activated with light(^max= 446 nm), to enter a series of transientintermediates that jointly form the photocycle of this photosensor protein.The most stable of these transient states is the signalling state forphototaxis, pB.The spatial structure of the ground state of PYP, pG and the spectralproperties of the photocycle intermediates have been very well resolved.Owing to its excellent chemical- and photochemical stability, also the spatialstructure of its photocycle intermediates has been characterised with X-raydiffraction and multinuclear NMR spectroscopy. Surprisingly, the resultsobtained showed that their structure is dependent on the molecular contextin which they are formed. Therefore, a large range of diffraction-,scattering- and spectroscopic techniques is now being employed to resolvein detail the dynamical changes of the structure of PYP while it progressesthrough its photocycle. This approach has led to considerable progress,although some techniques still result in mutually inconsistent conclusionsregarding aspects of the structure of particular intermediates.Recently, significant progress has also been made with simulations withmolecular dynamics analyses of the initial events that occur in PYP uponphoto activation. The great challenge in this field is to eventually obtainagreement between predicted dynamical alterations in PYP structure, asobtained with the MD approach and the actually measured dynamicalchanges in its structure as evolving during photocycle progression.