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排序方式: 共有224条查询结果,搜索用时 15 毫秒
91.
Gene-microarray analysis of multiple sclerosis lesions yields new targets validated in autoimmune encephalomyelitis 总被引:29,自引:0,他引:29
92.
Substrate binding and catalytic mechanism in ascorbate peroxidase: evidence for two ascorbate binding sites 总被引:1,自引:0,他引:1
The catalytic mechanism of recombinant soybean cytosolic ascorbate peroxidase (rsAPX) and a derivative of rsAPX in which a cysteine residue (Cys32) located close to the substrate (L-ascorbic acid) binding site has been modified to preclude binding of ascorbate [Mandelman, D., Jamal, J., and Poulos, T. L. (1998) Biochemistry 37, 17610-17617] has been examined using pre-steady-state and steady-state kinetic techniques. Formation (k1 = 3.3 +/- 0.1 x 10(7) M(-1) s(-1)) of Compound I and reduction (k(2) = 5.2 +/- 0.3 x 10(6) M(-1) s(-1)) of Compound I by substrate are fast. Wavelength maxima for Compound I of rsAPX (lambda(max) (nm) = 409, 530, 569, 655) are consistent with a porphyrin pi-cation radical. Reduction of Compound II by L-ascorbate is rate-limiting: at low substrate concentration (0-500 microM), kinetic traces were monophasic but above approximately 500 microM were biphasic. Observed rate constants for the fast phase overlaid with observed rate constants extracted from the (monophasic) dependence observed below 500 microM and showed saturation kinetics; rate constants for the slow phase were linearly dependent on substrate concentration (k(3-slow)) = 3.1 +/- 0.1 x 10(3) M(-1) s(-1)). Kinetic transients for reduction of Compound II by L-ascorbic acid for Cys32-modified rsAPX are monophasic at all substrate concentrations, and the second-order rate constant (k(3) = 0.9 +/- 0.1 x 10(3) M(-1) s(-1)) is similar to that obtained from the slow phase of Compound II reduction for unmodified rsAPX. Steady-state oxidation of L-ascorbate by rsAPX showed a sigmoidal dependence on substrate concentration and data were satisfactorily rationalized using the Hill equation; oxidation of L-ascorbic acid by Cys32-modified rsAPX showed no evidence of sigmoidal behavior. The data are consistent with the presence of two kinetically competent binding sites for ascorbate in APX. 相似文献
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Hodkinson PS Elliott PA Lad Y McHugh BJ MacKinnon AC Haslett C Sethi T 《The Journal of biological chemistry》2007,282(39):28991-29001
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Heena V. Lad Lin Liu José L. Payá-Cano Cathy Fernandes Leonard C. Schalkwyk 《Mammalian genome》2007,18(6-7):482-491
Immobility in the tail suspension test (TST) is considered a model of despair in a stressful situation, and acute treatment
with antidepressants reduces immobility. Inbred strains of mouse exhibit widely differing baseline levels of immobility in
the TST and several quantitative trait loci (QTLs) have been nominated. The labor of manual scoring and various scoring criteria
make obtaining robust data and comparisons across different laboratories problematic. Several studies have validated strain
gauge and video analysis methods by comparison with manual scoring. We set out to find objective criteria for automated scoring
parameters that maximize the biological information obtained, using a video tracking system on tapes of tail suspension tests
of 24 lines of the BXD recombinant inbred panel and the progenitor strains C57BL/6J and DBA/2J. The maximum genetic effect
size is captured using the highest time resolution and a low mobility threshold. Dissecting the trait further by comparing
genetic association of multiple measures reveals good evidence for loci involved in immobility on chromosomes 4 and 15. These
are best seen when using a high threshold for immobility, despite the overall better heritability at the lower threshold.
A second trial of the test has greater duration of immobility and a completely different genetic profile. Frequency of mobility
is also an independent phenotype, with a distal chromosome 1 locus.
Electronic supplementary material The online version of this article (doi: ) contains supplementary material, which is available to authorized users. 相似文献
97.
Haem peroxidases catalyse the H2O2-dependent oxidation of a variety of, usually organic, substrates. Mechanistically, these enzymes are very well characterized: they share a common catalytic cycle that involves formation of a two-electron oxidized intermediate (Compound I) followed by reduction of Compound I by substrate. The substrate specificity is more diverse, however. Most peroxidases oxidize small organic substrates, but there are prominent exceptions to this and the structural features that control substrate specificity remain poorly defined. APX (ascorbate peroxidase) catalyses the H2O2-dependent oxidation of L-ascorbate and has properties that place it at the interface between the class I (e.g. cytochrome c peroxidase) and classical class III (e.g. horseradish peroxidase) peroxidase enzymes. We present a unified analysis of the catalytic and substrate-binding properties of APX, including the crystal structure of the APX-ascorbate complex. Our results provide new rationalization of the unusual functional features of the related cytochrome c peroxidase enzyme, which has been a benchmark for peroxidase-mediated catalysis for more than 20 years. 相似文献
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