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1.
2.
Free radical mechanisms in enzyme reactions 总被引:1,自引:0,他引:1
Isao Yamazaki 《Free radical biology & medicine》1987,3(6):397-404
Free radicals are formed in prosthetic groups or amino acid residues of certain enzymes. These free radicals are closely related to the activation process in enzyme catalysis, but their formation does not always result in the formation of substrate free radicals as a product of the enzyme reactions. The role of free radicals in enzyme catalysis is discussed. 相似文献
3.
Zhenbo Cao Suraj Subramaniam Neil J. Bulleid 《The Journal of biological chemistry》2014,289(9):5490-5498
Typical 2-Cys peroxiredoxins are required to remove hydrogen peroxide from several different cellular compartments. Their activity can be regulated by hyperoxidation and consequent inactivation of the active-site peroxidatic cysteine. Here we developed a simple assay to quantify the hyperoxidation of peroxiredoxins. Hyperoxidation of peroxiredoxins can only occur efficiently in the presence of a recycling system, usually involving thioredoxin and thioredoxin reductase. We demonstrate that there is a marked difference in the sensitivity of the endoplasmic reticulum-localized peroxiredoxin to hyperoxidation compared with either the cytosolic or mitochondrial enzymes. Each enzyme is equally sensitive to hyperoxidation in the presence of a robust recycling system. Our results demonstrate that peroxiredoxin IV recycling in the endoplasmic reticulum is much less efficient than in the cytosol or mitochondria, leading to the protection of peroxiredoxin IV from hyperoxidation. 相似文献
4.
边缘性缺乏抗坏血酸之豚鼠,于三周内其肝脏及小肠粘膜3-羟-3-甲基戊二酰辅酶A还原酶(HMGR)活力均下降到原有水平的50%,但肝脏胆固醇7α-羟化酶活力尚无显著性改变。坏血病豚鼠(三周内)上述几种酶活力都下降至原有水平的50%左右。豚鼠摄取抗坏血酸不足,其血清总胆固醇浓度显著增加,而血清高密度脂蛋自胆固醇浓度显著减少,其改变程度与抗坏血酸缺乏状况一致。 相似文献
5.
本文报道人疱疹病豢-6型(HHV-6)pSTY28DNA片段的序列测定。应用分子克隆、缺损突变体(Dcletionmutant)制备和序列测定等技术,完成了3.9kbHHV-6pSTY28DNA片段的全序列测定。经DNASIS核酸蛋白软件分析,该片段含有两个开读框架(ORF)核糖核苷酸还原酶(RIR)ORF有2414个核苷酸,可编码805个氨基酸;P41蛋白由1100个核苷酸组成。与其他疱疹病毒作氨基酸同源性比较,HHV-6RiR与人巨细胞病毒(HCMV)有高度同源性,最适记分(Optimizedscore)达459。实验结果支持Esftathiou提出的论点,HHV-6属于β-疱疹病毒。 相似文献
6.
T. M. Hennessey L. E. Frego J. T. Francis 《Journal of comparative physiology. A, Neuroethology, sensory, neural, and behavioral physiology》1994,175(5):655-665
Paramecium is a valuable eukaryotic model system for studying chemosensory transduction, adaptation and cellular sensory integration. While millimolar amounts of many attractants hyperpolarize and cause faster forward swimming, oxidants are repellents that depolarize and cause backward swimming at micromolar concentrations. The non-permeant oxidants cytochrome c, nitro blue tetrazolium and ferricyanide are repellents with half maximal concentrations of 0.4 M, 2.2 M and 100 M respectively. In vivo reductase activities follow the same order of potencies. The concentration dependence of the cytochrome c reductase activity is well correlated with cytochrome c-induced depolarizations. This suggests that plasma membrane reduction of external cytochrome c is electrogenic, causing membrane depolarization and chemorepulsion. The reductase activity also appears to be voltage dependent. Depolarization by either K+, Na+, Ca+ or Mg+ correlates with inhibition of both in vivo reductase activities and cytochrome c-induced membrane potential changes. These responses were also seen in deciliated cells, showing that the body plasma membrane is sufficient for the response. Both chloroquine and diphenyleneiodonium inhibited reductase activities but only at unusually high concentrations. This activity showed no pH dependence in the physiological range. We propose that a plasma membrane bound NADPH-dependent reductase controls oxidant-induced depolarizations and consequent chemorepulsion.Abbreviations
bmv
Body plasma membrane vesicles
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BPS
Bathophenanthroline disulfonate
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cAMP
Cyclic adenosine monophosphate
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cmv
Ciliary membrane vesicles
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cyt c
Cytochrome c
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DPI
Diphenyleneiodonium
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EC
50
Concentration for 50% effectiveness
-
FeCN
Ferricyanide [Fe(CN)6–3]
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FeEDTA
Ethylenediaminetetracetic acid (ferric-sodium salt)
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GTP
Guanosine 5-triphosphate
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KCN
Potassium cyanide
-
mM
Millimolar
-
MOPS
3-(N-morpholino) propanesulfonic acid
-
mV
Millivolts
-
NADH
Nicotinamide adenine dinucleotide (reduced form)
-
NADPH
Nicotinamide adenine dinucleotide phosphate (reduced form)
-
NBT
Nitro blue tetrazolium
-
nm
Nanometer
-
pCMB
p-Chloromercuribenzoate
-
PMA
Phorbol 12-myristate 13-acetate
-
s.d.
Standard deviation
-
SOD
Superoxide dismutase
-
Tris
Tris(hydroxymethyl)aminomethane
-
M
Micromolar 相似文献
7.
NADPH-cytochrome P450 reductase was purified to apparent homogeneity and cytochrome P450 partially purified from whole rat brain. Purified reductase from brain was identical to liver P450 reductase by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and western blot techniques. Kinetic studies using cerebral P450 reductase reveal Km values in close agreement with those determined with enzyme purified from rat liver. Moreover, the brain P450 reductase was able to function successfully in a reconstituted microsomal system with partially purified brain cytochrome P450 and with purified hepatic P450c (P450IA1) as measured by 7-ethoxycoumarin and 7-ethoxyresorufin O-deethylation. Our results indicate that the reductase and P450 components may interact to form a competent drug metabolism system in brain tissue. 相似文献
8.
《Free radical research》2013,47(6):403-408
In the mid-fifth instar larvae of the cabbage looper moth, Trichoplusia ni, the subcellular distribution of total superoxide dismutase was as follows: 3.05 units (70.0%), 0.97 units (22.3%), and 0.33 units (7.6%) mg?1 protein in the mitochondrial, cytosolic and nuclear fractions, respectively. No superoxide dismutase activity was detected in the microsomal fraction. Catalase activity was unusually high and as follows: 283.4 units (47.3%), 150.1 units (25.1%). 142.3 units (23.8%), and 22.9 units (3.8%) mg?1 protein in the mitochondrial, cytosolic, microsomal (containing peroxisomes), and nuclear fractions. No glutathione peroxidase activity was found, but appreciable glutathione reductase activity was detected with broad subcellular distribution as follows: 3.86 units (36.1%), 3.68 units (34.0%). 2.46 units (23.0%). and 0.70 units (6.5%) mg?1 protein in the nuclear, mitochondrial, and cytosolic fractions, respectively. The unusually wide intracellular distribution of catalase in this phytophagous insect is apparently an evolutionary adaptation to the absence of glutathione peroxidase; hence, lack of a glutathione peroxidase-glutathione reductase role in alleviating stress from lipid peroxidation. Catalase working sequentially to superoxide dismutase, may nearly completely prevent the formation of the lipid peroxidizing OH radical from all intracellular compartments by the destruction of H2O2 which together with O?2 is a precursor of OH. 相似文献
9.
Yorishige Imamura Toshihisa Koga Hideaki Shimada Masaki Otagiri 《Journal of enzyme inhibition and medicinal chemistry》2013,28(1):35-39
The chemical modifications of rabbit liver carbonyl reductase (RLCR) with phenylglyoxal (PGO) and 2,3,4-trinitrobenzenesulfonate sodium (TNBS), which are respective chemical modifiers of arginine and lysine residues, were examined. RLCR was rapidly inactivated by these modifiers. Kinetic data for the inactivation demonstrated that each one of arginine and lysine residues is essential for catalytic activity of the enzyme. Furthermore, based on the protective effects of NADP +, NAD + and their constituents against the inactivation of RLCR by PGO and TNBS, we propose the possibility that the functional arginine and lysine residues are located in the coenzyme-binding domain of RLCR and interact with the 2′-phosphate group of NADPH. 相似文献
10.