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排序方式: 共有231条查询结果,搜索用时 15 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
2.
The multiple isotope effect method of Hermes et al. [Hermes, J. D., Roeske, C. A., O'Leary, M. H., & Cleland, W. W. (1982) Biochemistry 21, 5106-5114] has been used to study the mechanism of the oxidative decarboxylation catalyzed by 6-phosphogluconate dehydrogenase from yeast. 13C kinetic isotope effects of 1.0096 and 1.0081 with unlabeled or 3-deuterated 6-phosphogluconate, plus a 13C equilibrium isotope effect of 0.996 and a deuterium isotope effect on V/K of 1.54, show that the chemical reaction after the substrates have bound is stepwise, with hydride transfer preceding decarboxylation. The kinetic mechanism of substrate addition is random at pH 8, since the deuterium isotope effect is the same when either NADP or 6-phosphogluconate or 6-phosphogluconate-3-d is varied at fixed saturating levels of the other substrate. Deuterium isotope effects on V and V/K decrease toward unity at high pH at the same time that V and V/K are decreasing, suggesting that proton removal from the 3-hydroxyl may precede dehydrogenation. Comparison of the tritium effect of 2.05 with the other measured isotope effects gives limits of 3-4 on the intrinsic deuterium and of 1.01-1.05 for the intrinsic 13C isotope effect for C-C bond breakage in the forward direction and suggests that reverse hydride transfer is 1-4 times faster than decarboxylation. 相似文献
3.
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.
Dr AR Holmes RD Cannon HF Jenkinson 《Journal of industrial microbiology & biotechnology》1995,15(3):208-213
The yeastCandida albicans coaggregates with a variety of streptococcal species, an interaction that may promote oral colonization by yeast cells.C. albicans andCandida tropicalis are the yeasts most frequently isolated from the human oral cavity and our data demonstrate that both these species bind toStreptococcus gordonii NCTC 7869 while two otherCandida species (Candida krusei andCandida kefyr) do not. Adherence ofC. albicans was greatest when the yeast had been grown at 30° C to mid-exponential growth phase. For 21 strains ofC. albicans there was a positive correlation between the ability to adhere toS. gordonii and adherence to experimental salivary pellicle. Whole saliva either stimulated or slightly inhibited adherence ofC. albicans toS. gordonii depending on the streptococcal growth conditions. The results suggest that the major salivary adhesins and coaggregation adhesins ofC. albicans are co-expressed. 相似文献
5.
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
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.
9.
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
10.
Gene therapy of erectile dysfunction in the rat with penile neuronal nitric oxide synthase 总被引:3,自引:0,他引:3
Magee TR Ferrini M Garban HJ Vernet D Mitani K Rajfer J Gonzalez-Cadavid NF 《Biology of reproduction》2002,67(3):1033-1041
Gene transfer to the penile corpora cavernosa of constructs of the inducible and endothelial nitric oxide synthase (NOS) cDNAs ameliorates erectile dysfunction in aged rats. In this study, we investigated whether the neuronal NOS (nNOS) variant responsible for erection, penile nNOS (PnNOS), can exert a similar effect, and whether the combination of electroporation with a helper-dependent adenovirus (AdV) improves gene transfer. PnNOS and beta-galactosidase cDNAs were cloned in plasmid (pCMV-PnNOS; pCMV-beta-gal) and "gutless" AdV (AdV-CMV-PnNOS; AdV-CMV-beta-gal) vectors, and injected into the penis of adult (beta-gal) or aged (PnNOS) rats, with or without electroporation. Penile erection was measured at different times after PnNOS cDNA injection, by electrical field stimulation of the cavernosal nerve. The expression of beta-galactosidase or PnNOS was estimated in penile tissue by either histochemistry and luminometry or Western blot, and the effects of AdV-CMV-PnNOS on mRNA expression were examined by a DNA microarray. We found that electroporation increased pCMV-beta-gal uptake, and its expression was detectable at 56 days. In the aged rats treated with pCMV-PnNOS and electroporation, the maximal intracavernosal:mean arterial pressure ratios were elevated for 11 and 18 days when compared with those in controls. Electroporation intensified penile uptake of as few as 10(6) viral particles (vp) of AdV-CMV-beta-gal, and with 10(7) vp beta-galactosidase was still detectable at 60 days. Electroporated AdV-CMV-PnNOS (10(7) vp) was effective at 18 days in stimulating the erection of aged rats, without inducing the expression of cytotoxic genes. In conclusion, intracavernosal gene therapy with PnNOS cDNA corrected the aging-related erectile dysfunction for at least 18 days when given by electroporation in a helper-dependent AdV at low viral loads. 相似文献