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141.
Isabel Moura Sofia R. Pauleta José J. G. Moura 《Journal of biological inorganic chemistry》2008,13(8):1185-1195
Metalloenzymes control enzymatic activity by changing the characteristics of the metal centers where catalysis takes place.
The conversion between inactive and active states can be tuned by altering the coordination number of the metal site, and
in some cases by an associated conformational change. These processes will be illustrated using heme proteins (cytochrome
c nitrite reductase, cytochrome c peroxidase and cytochrome cd
1 nitrite reductase), non-heme proteins (superoxide reductase and [NiFe]-hydrogenase), and copper proteins (nitrite and nitrous
oxide reductases) as examples. These examples catalyze electron transfer reactions that include atom transfer, abstraction
and insertion. 相似文献
142.
Ivanov AE Thammakhet C Kuzimenkova MV Thavarungkul P Kanatharana P Mikhalovska LI Mikhalovsky SV Galaev IY Mattiasson B 《Journal of molecular recognition : JMR》2008,21(2):89-95
Radical copolymerization of acrylamide (Am) (90 mol%) with N-acryloyl-m-aminophenylboronic acid (NAAPBA) (10 mol%) carried out on the surface of glass slides in aqueous solution and in the absence of chemical cross-linkers, resulted in the formation of thin semitransparent gels. The phenylboronic acid (PBA) ligand density was ca. 160 micromol/ml gel. The gels exhibited a macroporous structure and displayed optical response to sucrose, lactose, glucose and fructose in 50 mM sodium phosphate buffer, in the pH range from 6.5 to 7.5. The response was fairly reversible and linearly depended on glucose concentration in the wide concentration range from 1 to 60 mM at pH 7.3. The character of response was explained by the balance of two competing equilibrium processes: binding of glucose to phenylboronate anions and binary hydrophobic interactions of neutral PBA groups. The apparent diffusion coefficient of glucose in the gels was ca. 2.5 x 10(-7) cm(2)/s. A freshly prepared gel can be used daily for at least 1 month without changes in sensitivity. Autoclaving (121 degrees C, 1.2 bar, 10 min) allows for the gels sterilization, which is important for their use as glucose sensors in fermentation processes. 相似文献
143.
N. A. Kas’yanenko N. B. Zakharova D. A. Mukhin A. V. Slita O. V. Nazarova E. A. Leont’eva E. F. Panarin 《Biophysics》2008,53(1):31-37
Generation and physicochemical properties of complexes formed by high-molecular thymus DNA and plasmid DNA with synthetic polymers of (dimethyl amino)ethyl methacrylate, (diethyl amino)ethyl methacrylate, and poly(vinyl amine) were studied in solutions of different ionic strength using low-gradient viscometry, electrophoresis, circular dichroism, spectrophotometry, and dynamic light scattering. The complexes were tested for toxicity with T98G cell cultures. Condensation of DNA was shown to occur when the ratio of charged groups in the polycations and DNA exceeded unity. This condensation manifested itself as an increase in the optical density of DNA solutions. Condensation-associated changes in the dimensions of DNA molecules were determined, and phase diagrams of DNA-polycation systems were analyzed in the presence of NaCl. MTT analysis revealed no toxicity of these complexes. 相似文献
144.
Laiyong Mu Roy E. Ritzmann 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》2008,194(3):283-298
Tethered cockroaches turn from unilateral antennal contact using asymmetrical movements of mesothoracic (T2) legs (Mu and
Ritzmann in J Comp Physiol A 191:1037–1054, 2005). During the turn, the leg on the inside of the turn (the inside T2 leg) has distinctly different motor patterns from those
in straight walking. One possible neural mechanism for the transformation from walking to inside leg turning could be that
the descending commands alter a few critical reflexes that start a cascade of physical changes in leg movement or posture,
leading to further alterations. This hypothesis has two implications: first, the descending activities must be able to influence
thoracic reflexes. Second, one should be able to initiate the turning motor pattern without descending signals by mimicking
a point farther down in the reflex cascade. We addressed the first implication in this paper by experiments on chordotonal
organ reflexes. The activity of depressor muscle (Ds) and slow extensor tibia muscle (SETi) was excited and inhibited by stretching
and relaxing the femoral chordotonal organ. However, the Ds responses were altered after eliminating the descending activity,
while the SETi responses remain similar. The inhibition to Ds activity by stretching the coxal chordotonal organ was also
altered after eliminating the descending activity. 相似文献
145.
Walid Khemakhem Emna Ammar Amina Bakhrouf 《World journal of microbiology & biotechnology》2005,21(8-9):1623-1631
Summary Bioflocculation of bacteria isolated from the marine biomass acclimatized to textile wastewater has been achieved. Pseudomonas was the main genus found in the marine biomass. This bacterium showed an important hydrophobicity but slightly weaker than
that of pilot plant genera adapted to the conventional sewage. This hydrophobicity provided the bacteria with hydrophobic
characters, especially those of the polymeric extracellular substances (ECS) released in the sewage. Whereas some factors
such as the divalent cations, calcium and magnesium had an effect on this bacterial hydrophobicity, glucose concentration
did not have any impact. Furthermore, the physiological state of the cells hatched in the sewage had an impact on the hydrophobicity.
Indeed, during the logarithmic growth phase, cell hydrophobicity increase enhanced floc formation, thus improving wastewater
treatment. 相似文献
146.
Highly toxic beryllium(II) is divalent metal ion with a high charge density, making it a potential target for binding to bio-molecules rich in O donor groups. In aqueous solution Be2+ binds to ATP and ADP to form 1:1 Be2+:ATP and Be2+:ADP complexes in relatively acidic media. At neutral pH the complex formed undergoes hydrolysis. Be2+ binding to ATP and ADP is much stronger than Ca2+ and Mg2+ binding. The high affinity of Be2+ toward ATP and ADP binding suggests a mechanism relevant to understanding the in vivo chemical toxicity of this metal. 相似文献
147.
Low-temperature, single crystal X-ray structural characterisations of trans-[NiCl2(HOMe)4], trans-O-[Ni(MeOH)2(μ-Cl)(2/2)2](∞∣∞) · 0.5dioxan and trans-trans-[Ni(H2O)2Cl2(O-dioxan-O)(2/2)](∞∣∞) · dioxan are recorded, offering intriguing insights into O-donor/Ni(II) relativities. All nickel atoms in all structures are located on crystallographic inversion centres, the last two compounds being one-dimensional polymers. 相似文献
148.
生物可降解嵌段共聚物在给药载体中的应用 总被引:3,自引:0,他引:3
生物可降解嵌段聚合物因具有双亲性 ,靶向药物到特定部位等优点大大推动了作为给药载体系统的发展。本文综述了生物可降解嵌段聚合物在表面修饰、水凝胶、胶束、生物大分子载体系统中的应用 相似文献
149.
M. Tsaramyrsi D. Kavousanaki C. P. Raptopoulou A. Terzis A. Salifoglou 《Inorganica chimica acta》2001,320(1-2):47-59
The aqueous chemistry of vanadium with physiologically relevant ligands constitutes a subject of burgeoning research, extending from bacterial metalloenzymic functions to human-health physiology. Vanadium, in the form of VCl3 and V2O5, reacted expediently with citric acid, in a 1:2 molar ratio in water at pH4, and, in the presence of various cations, afforded crystalline materials bearing the general formula (Cat)2[V2O4(C6H6O7)2]·nH2O (A) (Cat+=Na+, NH4 +, n=2; Me4N+, K+, n=4). Exploration of the reactivity of A toward H2O2 yielded the peroxo-containing complexes (Cat)2[V2O2(O2)2(C6H6O7)2]·2H2O (B) (Cat+=K+, NH4 +). Both classes of compounds were characterized analytically and spectroscopically. The X-ray structures of complexes A and B emphasize the exceptional stability of the dimeric rhombic unit VV 2O2, which is retained upon H2O2 reaction, and the preserved mode of coordination of the citrate ligand as a doubly deprotonated moiety. In these complexes, typical six and eight coordination numbers were observed for the Na+ and K+ counter-ions, respectively. The variety of synthetic approaches leading to A, along with the stepwise and direct assembly and isolation of peroxo-compounds (B), denotes the significance of reaction pathways and intermediates in vanadium(III–V)–citrate synthetic chemistry. Hence, a systematic investigation of reactivity modes in aqueous vanadium–citrate systems emerges as a crucial tool for the establishment of chemical interconnectivity among low MW complex species, potentially participating in the intricate biodistribution of that metal ion in biological fluids. 相似文献
150.
We examined hand preferences in 23 tufted capuchins (Cebus apella) in 2 tasks requiring the lid of a box to be lifted before taking out a peanut. The first task, Box 1, could entail either 2 or 3 problem-solving acts, with the 3-act solution involving bimanual coordination for food retrieval. The second task, Box 2, involved only the 3-act solution. The results indicated that the types of solution employed to perform the task influenced capuchin hand preferences. In the 2-act solution, capuchins exhibited a significant right-hand bias for the final one-handed reaching action, but not for the initial lid lifting action. In contrast, in the 3-act solution, no significant asymmetry emerged for any act. We noted a significant effect of subject's sex on the strength of laterality, with males being more strongly lateralized than females. We discuss results in the light of recent models of primate laterality. 相似文献