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排序方式: 共有634条查询结果,搜索用时 21 毫秒
101.
Cuong Quang Le Mercy Oyugi Ebenezer Joseph Toan Nguyen Md Hasmat Ullah Joshua Aubert Thien Phan Joseph Tran Kayunta Johnson-Winters 《Biochemistry and Biophysics Reports》2017
F420H2:NADP+ Oxidoreductase (Fno) catalyzes the reversible reduction of NADP+ to NADPH by transferring a hydride from the reduced F420 cofactor. Here, we have employed binding studies, steady-state and pre steady-state kinetic methods upon wtFno and isoleucine 135 (I135) Fno variants in order to study the effects of side chain length on the donor-acceptor distance between NADP+ and the F420 precursor, FO. The conserved I135 residue of Fno was converted to a valine, alanine and glycine, thereby shortening the side chain length. The steady-state kinetic analysis of wtFno and the variants showed classic Michaelis-Menten kinetics with varying FO concentrations. The data revealed a decreased kcat as side chain length decreased, with varying FO concentrations. The steady-state plots revealed non-Michaelis-Menten kinetic behavior when NADPH was varied. The double reciprocal plot of the varying NADPH concentrations displays a downward concave shape, while the NADPH binding curves gave Hill coefficients of less than 1. These data suggest that negative cooperativity occurs between the two identical monomers. The pre steady-state Abs420 versus time trace revealed biphasic kinetics, with a fast phase (hydride transfer) and a slow phase. The fast phase displayed an increased rate constant as side chain length decreased. The rate constant for the second phase, remained ~2 s?1 for each variant. Our data suggest that I135 plays a key role in sustaining the donor-acceptor distance between the two cofactors, thereby regulating the rate at which the hydride is transferred from FOH2 to NADP+. Therefore, Fno is a dynamic enzyme that regulates NADPH production. 相似文献
102.
The influence of sodium and potassium dynamics on excitability,seizures, and the stability of persistent states: I. Single neuron dynamics 总被引:1,自引:1,他引:0
John R. CressmanJr. Ghanim Ullah Jokubas Ziburkus Steven J. Schiff Ernest Barreto 《Journal of computational neuroscience》2009,26(2):159-170
In these companion papers, we study how the interrelated dynamics of sodium and potassium affect the excitability of neurons,
the occurrence of seizures, and the stability of persistent states of activity. In this first paper, we construct a mathematical
model consisting of a single conductance-based neuron together with intra- and extracellular ion concentration dynamics. We
formulate a reduction of this model that permits a detailed bifurcation analysis, and show that the reduced model is a reasonable
approximation of the full model. We find that competition between intrinsic neuronal currents, sodium-potassium pumps, glia,
and diffusion can produce very slow and large-amplitude oscillations in ion concentrations similar to what is seen physiologically
in seizures. Using the reduced model, we identify the dynamical mechanisms that give rise to these phenomena. These models
reveal several experimentally testable predictions. Our work emphasizes the critical role of ion concentration homeostasis
in the proper functioning of neurons, and points to important fundamental processes that may underlie pathological states
such as epilepsy.
相似文献
John R. Cressman Jr.Email: |
103.
Gulay Bayramoglu Ihsan Gursel Yagmur Tunali M. Yakup Arica 《Bioresource technology》2009,100(10):2685-2691
The removal of phenol (Ph) and 2-chlorophenol (2-CPh) from aqueous solution by native and heat inactivated fungus Funaliatrogii pellets were investigated. The effects of contact time, solid/liquid ratio, optimum pH and temperature on the phenols removal capacity by the pellets were established. The removal efficiency of phenols increased significantly with increasing biomass dose. The optimum pH was detected to be 8.0. The second-order equations are described and evaluated on the basis of a comparative estimation of the corresponding coefficients. The phenol removal equilibrium isotherm was modeled by the Langmuir equations. The enthalpy change values were obtained between −7.62 and −10.64 kJ/mol. This indicated that the uptake of phenols either on native or heat inactivated fungal pellets was based on a physical adsorption process. 相似文献
104.
de Giuseppe PO Ullah A Silva DT Gremski LH Wille AC Chaves Moreira D Ribeiro AS Chaim OM Murakami MT Veiga SS Arni RK 《Biochemical and biophysical research communications》2011,409(4):6064-627
Phospholipases D (PLDs) are principally responsible for the local and systemic effects of Loxosceles envenomation including dermonecrosis and hemolysis. Despite their clinical relevance in loxoscelism, to date, only the SMase I from Loxosceles laeta, a class I member, has been structurally characterized. The crystal structure of a class II member from Loxosceles intermedia venom has been determined at 1.7 Å resolution. Structural comparison to the class I member showed that the presence of an additional disulphide bridge which links the catalytic loop to the flexible loop significantly changes the volume and shape of the catalytic cleft. An examination of the crystal structures of PLD homologues in the presence of low molecular weight compounds at their active sites suggests the existence of a ligand-dependent rotamer conformation of the highly conserved residue Trp230 (equivalent to Trp192 in the glycerophosphodiester phosphodiesterase from Thermus thermophofilus, PDB code: 1VD6) indicating its role in substrate binding in both enzymes. Sequence and structural analyses suggest that the reduced sphingomyelinase activity observed in some class IIb PLDs is probably due to point mutations which lead to a different substrate preference. 相似文献
105.
Ozdemir E Bagcivan I Durmus N Altun A Gursoy S 《Canadian journal of physiology and pharmacology》2011,89(2):89-95
Although the phenomenon of opioid tolerance has been widely investigated, neither opioid nor nonopioid mechanisms are completely understood. The aim of the present study was to investigate the role of the nitric oxide (NO)-cyclic guanosine monophosphate (cGMP) pathway in the development of morphine-induced analgesia tolerance. The study was carried out on male Wistar albino rats (weighing 180-210 g; n = 126). To develop morphine tolerance, animals were given morphine (50 mg/kg; s.c.) once daily for 3 days. After the last dose of morphine was injected on day 4, morphine tolerance was evaluated. The analgesic effects of 3-(5'-hydroxymethyl-2'-furyl)-1-benzylindazole (YC-1), BAY 41-2272, S-nitroso-N-acetylpenicillamine (SNAP), N(G)-nitro-L-arginine methyl ester (L-NAME), and morphine were considered at 15 or 30 min intervals (0, 15, 30, 60, 90, and 120 min) by tail-flick and hot-plate analgesia tests (n = 6 in each study group). The results showed that YC-1 and BAY 41-2272, a NO-independent activator of soluble guanylate cyclase (sGC), significantly increased the development and expression of morphine tolerance, and L-NAME, a NO synthase (NOS) inhibitor, significantly decreased the development of morphine tolerance. In conclusion, these data demonstrate that the nitric oxide-cGMP signal pathway plays a pivotal role in developing tolerance to the analgesic effect of morphine. 相似文献
106.
Sultana Juhara Mannan Mohammad Abul Kalam Azad Md. Ashik Ullah Abdullah Al Maruf Md. Israt Rayhan Mohammad Shamsul Ahsan Abul Hasnat 《Biological trace element research》2011,140(3):272-283
Drug abuser patients (n = 104), age ranging from 19 to 42 years, were randomly recruited to investigate the serum levels of trace elements (Cu, Zn,
Fe, and Mg), malondialdehyde (MDA), and immunoglobulin (IgG, IgA, and IgM) before and after clinical intervention. Control
group also included 104 healthy individuals. Blood samples were analyzed for determining trace elements, MDA, and immunoglobulin
using atomic absorption spectroscopy, Ultraviolet-Visible (UV-VIS) spectroscopy, and turbidimetry method, respectively. For
serum level of Zn and Fe, the differences between the groups (before intervention, after intervention, and control) were not
significant (p > 0.05). However, significant differences were found in serum copper levels between control group, drug abuser patients,
and before and after intervention (p < 0.05). The concentration of Mg was found to be significantly higher (p = 0.007) in drug abuser patients than the controls, and after intervention, the level was restored to control value. A displacement
of elemental homeostasis was observed in drug abuser patients compared to control, and it was improved after intervention.
An increase in serum concentration of MDA was found in drug abuser patients compared to control subjects (p > 0.05) but was not statistically significant. After intervention, the concentration was restored to control value (p > 0.05). The serum concentrations of IgA and IgM were found to be significantly higher (p < 0.05) in drug abuser patients before intervention than the controls, and the level tended to be restored to control level
after clinical intervention. Serum IgG level was found to be lower in drug abuser patients compared to controls and further
declined significantly (p < 0.05) after intervention. These findings may suggest a possible imbalance in the levels of micronutrients, antioxidants,
and immunoglobulin in drug abuser patients, which tend to be restored to control values after detoxification. 相似文献
107.
We investigated the effect of temperature on development and demographic parameters such as the intrinsic rate of natural
increase (r
m) of the two spider mite species Tetranychus merganser Boudreaux and T. kanzawai Kishida at eleven constant temperatures ranging from 15 to 40°C at intervals of 2.5°C. Both male and female T. merganser and T. kanzawai completed development from egg to adult at temperatures ranging from 15 to 37.5°C. The longest developmental duration of
immature stages was found at 15°C and the shortest developmental duration was found at 35°C for both species. Using linear
and non-linear developmental rate models, the lower thermal thresholds for egg-to-adult (female and male) and egg-to-egg development
were estimated as 12.2–12.3°C for T. merganser and as 10.8°C for T. kanzawai. The highest developmental rates were observed at around 35°C, whereas the upper developmental thresholds were around 40°C
for both species. In fact, at 40°C, a few eggs of either species hatched, but no larvae reached the next stage. The r
m-values of T. merganser ranged from 0.072 (15°C) to 0.411 day−1 (35°C), whereas those of T. kanzawai ranged from 0.104 (15°C) to 0.399 (30°C). The r
m-values were higher for T. kanzawai than for T. merganser at temperatures from 15 to 30°C, but not at 35°C (0.348 day−1). Total fecundity of T. merganser was also higher than that of T. kanzawai at 35°C. These results indicate that higher temperatures favor T. merganser more than T. kanzawai. 相似文献
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