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排序方式: 共有241条查询结果,搜索用时 31 毫秒
1.
Evidence from nitrogen-15 and solvent deuterium isotope effects on the chemical mechanism of adenosine deaminase 总被引:1,自引:0,他引:1
We have determined 15N isotope effects and solvent deuterium isotope effects for adenosine deaminase using both adenosine and the slow alternate substrate 7,8-dihydro-8-oxoadenosine. With adenosine, 15N isotope effects were 1.0040 in H2O and 1.0023 in D2O, and the solvent deuterium isotope effect was 0.77. With 7,8-dihydro-8-oxoadenosine, 15N isotope effects were 1.015 in H2O and 1.0131 in D2O, and the solvent deuterium isotope effect was 0.45. The inverse solvent deuterium isotope effect shows that the fractionation factor of a proton, which is originally less than 0.6, increases to near unity during formation of the tetrahedral intermediate from which ammonia is released. Proton inventories for 1/V and 1/(V/K) vs percent D2O are linear, indicating that a single proton has its fractionation factor altered during the reaction. We conclude that a sulfhydryl group on the enzyme donates its proton to oxygen or nitrogen during this step. pH profiles with 7,8-dihydro-8-oxoadenosine suggest that the pK of this sulfhydryl group is 8.45. The inhibition of adenosine deaminase by cadmium also shows a pK of approximately 9 from the pKi profile. Quantitative analysis of the isotope effects suggests an intrinsic 15N isotope effect for the release of ammonia from the tetrahedral intermediate of approximately 1.03 for both substrates; however, the partition ratio of this intermediate for release of ammonia as opposed to back-reaction is 14 times greater for adenosine (1.4) than for 7,8-dihydro-8-oxoadenosine (0.1).(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
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A second form of hereditary chondrodystrophy (ch-2) has been discovered in a selected line of Japanese quail, Coturnix japonica. This form of chondrodystrophy is autosomal and recessive, characterized by an overall shortening and bending of the long bones of the wings and legs, slight dwarfing of the trunk, bulging of the eyes, flattening of the head, and a parrot beak. The shortened long bones vary in regard to the amount of bending from nearly straight to bends of up to 90 degrees in the midshaft region. In severe cases, the bend is evident as a protuberance of the skin. Affected embryos usually survive the 18-day incubation period. Several have hatched, but most survived no longer than 4 days after hatching. Only one female has survived long enough to lay eggs. Testcrosses indicated that this mutation is not allelic to micromelia. 相似文献
4.
Hermes HF Sonke T Peters PJ van Balken JA Kamphuis J Dijkhuizen L Meijer EM 《Applied and environmental microbiology》1993,59(12):4330-4334
An l-aminopeptidase of Pseudomonas putida, used in an industrial process for the hydrolysis of d,l-amino acid amide racemates, was purified to homogeneity. The highly l-enantioselective enzyme resembled thiol reagent-sensitive alkaline serine proteinases and was strongly activated by divalent cations. It possessed a high substrate specificity for dipeptides and alpha-H amino acid amides, e.g., l-phenylglycine amide. 相似文献
5.
Ankur Srivastava Gargi Mishra Kshitij RB Singh Jay Singh Rampal Pandey Mrituanjay D. Pandey 《Luminescence》2023,38(7):1347-1357
Rare earth metals play a conspicuous role in magnetic resonance imaging (MRI) for detecting cancerous cells. The alkali metal potassium is a neurotransmitter in the sodium–potassium pump in biomedical sciences. This unique property of rare earth metals and potassium drew our attention to carry forward this study. Therefore, in this work, previously synthesized potassium (K) complexes formed by the reflux of 4-N,N-dimethylaminobenzoic acid (DBA) and potassium hydroxide in methanol, and named [(μ2–4-N,N-dimethylaminobenzoate-κO)(μ2–4-N,N-dimethylaminobenzoic acid-κO)(4-N,N-dimethylaminobenzoic acid-κO) potassium(I) coordination polymer)] were treated hydrothermally with La2O3 nanomaterials to obtain a nanohybrid La2O3/K-complex. After that, the K-complex was analyzed using single-crystal X-ray diffraction and 1H and 13C NMR spectroscopy. In addition, the structural and morphological properties of the as-prepared nanostructured La2O3/K-complex were also characterized, which involved an investigation using X-ray diffraction (XRD)spectroscopy, Fourier transform infrared (FTIR) spectroscopy, atomic force spectroscopy (AFM), transmission electron microscopy (TEM), and energy dispersive X-ray (EDX) analysis. After this, the electrochemical redox behaviour of the synthesized nanohybrid material was studied using cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Therefore, the results from these studies revealed that the as-prepared material was a La2O3/K-complex that has a promising future role in sensing various analytes, as it showed effective electrocatalytic behaviour. 相似文献
6.
Peter Schneider Manfred Hermes 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1976,106(1):39-49
The function of the flapping elytra was investigated in garden shafers (Melolontha melolontha L.) and rhinoceros beetles (Oryctes boas Fabr.).
相似文献
1. | The movements of alae and elytra are determined. Both move with the same frequency and in the same phase, but the range of the elytral stroke never reaches below the frontal plane. In downstroke the elytra are at an angle positive to the airstream (horizontal flight). |
2. | After exact investigation of the construction of the elytra (depth, width, length, surface, torsion and velocity of each point of the elytra) the most effective point in the production of lift during the downstroke was determined. |
3. | After loss of one third of the surface of the elytra the beetles cannot fly horizontally. In tethered flight the wing stroke frequency of the alae does not increase when the elytra are shortened. Shortening of the elytra does not interfere with the resonance system of the pterothorax. |
4. | The lift of the elytra results from active and passive components (more than 17% of the body weight). In the airstream (front 2.00 m/s, average body weight 944 mp) the passive lift is 14.3% for elytra in the down position; 3.1% of the lift is caused by the active downstroke. |
5. | The elytra of these beetles are indispensible for horizontal flight. Primarily they produce lift passively with added help from the downstroke, and have no function for the drag. The effect of upstroke is discussed. |
7.
Wenjing Li Piotr Łączyński Hermes E. Escalona Jonas Eberle Lizhi Huo Xiaosheng Chen Weidong Huang Bingxu Chen Dirk Ahrens Adam Ślipiński Wioletta Tomaszewska Xingmin Wang 《Systematic Entomology》2020,45(2):447-463
Ladybirds of the cosmopolitan tribe Chilocorini prey mainly on coccids and include several important biocontrol agents. The phylogenetic relationships of Chilocorini are poorly known. In this paper, we provide a phylogenetic reconstruction of Chilocorini containing all 27 genera based on five molecular markers and 86 adult morphological characters. Morphological character states were mapped on the combined data tree from Bayesian inference to analyse morphological traits of each genus. Sixteen morphological characters were selected to reconstruct the ancestral states using maximum parsimony and maximum likelihood methods. Divergence times were estimated based on the relaxed molecular clock approach. Our results indicate that Chilocorini, excluding Chilocorellus Miyatake, is monophyletic and closely related to Plotinini. The crown group Chilocorini was estimated to date back to the Middle Cretaceous. Anisorcus Crotch, Egius Mulsant, Phaenochilus Weise and Simmondsius Ahmad & Ghani are synonymized here with Chilocorus Leach ( syn.n. ). The genus Chilocorellus is excluded from Chilocorini. The split of current genera was estimated to have occurred during the Middle Paleogene to Late Paleogene. 相似文献
8.
Two silicone coatings have been evaluated for barnacle adhesion. One coating is an unfilled hydrosilation cured polydimethylsiloxane (PDMS) network, while the other is a room temperature vulcanized (RTV), filled, ethoxysiloxane cured PDMS elastomer, RTV11?. The adhesion strength of one species of barnacle, Balanus eburneus, to the hydrosilation coatings is in the range of 0.37–0.60 kg cm‐2 while the corresponding range for RTV11 is 0.64–0.90 kg cm‐2. The easier release of B. eburneus from the hydrosilation cured network compared to RTV11 is discussed in relationship to differences in bulk and surface properties. Preliminary results suggest bulk modulus may be the most important parameter in determining barnacle adhesion strength. In light or mechanical property analysis, a re‐evaluation of surface properties and chemical stability is presented. 相似文献
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10.
de Meneses Alessandra Cristina Lerin Lindomar Alberto Araújo Pedro Henrique Hermes Sayer Cláudia de Oliveira Débora 《Bioprocess and biosystems engineering》2019,42(10):1625-1634
Bioprocess and Biosystems Engineering - In this work, a fed-batch approach was adopted to overcome propionic acid lipase inactivation effects in the benzyl propionate direct esterification mediated... 相似文献