水稻不育花药中H_2O_2的积累与膜脂过氧化的加剧

水稻7017、二九矮细胞质雄性不育系及其保持系花药的POD,CAT和SOD活性研究的结果表明,单核早期时不育及可育花药的酶活性差异不明显,单核晚期、二核及三核期的不育花药显著低于可育花药。在不育花药中缺少两条Cu-Zn SOD同工酶带,而且O_2~ 产生效率为可育的4.1～5.5倍,并有H_2O_2和MDA的积累。不育花药中H_2O_2的积累和膜脂过氧化的加剧可能与花粉败育有关。     

利用腺病毒DNA与爪蟾卵提取物在非细胞体系中重构细胞核(简报)

1983年,Lohka和Masui首先报道,用精子染色质与卵提取物一起温育,可以组装成具有典型结构的细胞核。这种核不仅具有合成DNA的能力,而且还能进入M期。同年,     

Effect of lead on blood protoporphyrin levels of a group of ring teal ducks (Callonetta leucophrys)

This research determined the relationships between blood lead level and zinc protoporphyrin (ZnPROTO), protoporphyrin IX (PROTO), and free erythrocyte protoporphyrin (FEP) levels in a group of 18 ring teal ducks. Blood samples were drawn from two groups of ring teal ducks as part of the routine health maintenance program of the New York Zoological Park. One group of six teals had been exposed to what is believed to be lead-contaminated dust, while the second group of twelve teals was unexposed. Blood samples were analyzed for lead by flameless atomic absorption and for protoporphyrins by fluorescence. Blood lead level and log blood lead level had positive correlations with each of the protoporphyrins: the logarithmic correlations were better than the nonlogarithmic correlations, and PROTO correlated better than ZnPROTO. With one exception, PROTO levels were higher than ZnPROTO levels. The results suggest that PROTO, FEP, or ZnPROTO could serve as a biological indicator of lead poisoning in ring teal ducks.     

Use of restrained molecular dynamics in water to determine three-dimensional protein structure: prediction of the three-dimensional structure of Ecballium elaterium trypsin inhibitor II

Refinement of distance geometry (DG) structures of EETI-II (Heitz et al.: Biochemistry 28:2392-2398, 1989), a member of the squash family trypsin inhibitor, have been carried out by restrained molecular dynamics (RMD) in water. The resulting models show better side chain apolar/polar surface ratio and estimated solvation free energy than structures refined "in vacuo." The consistent lower values of residual NMR constraint violations, apolar/polar surface ratio, and solvation free energy for one of these refined structures allowed prediction of the 3D folding and disulfide connectivity of EETI-II. Except for the few first residues for which no NMR constraints were available, this computer model fully agreed with X-ray structures of CMTI-I (Bode et al.: FEBS Lett. 242:285-292, 1989) and EETI-II complexed with trypsin that appeared after the RMD simulation was completed. Restrained molecular dynamics in water is thus proved to be highly valuable for refinement of DG structures. Also, the successful use of apolar/polar surface ratio and of solvation free energy reinforce the analysis of Novotny et al. (Proteins 4:19-30, 1988) and shows that these criteria are useful indicators of correct versus misfolded models.     

Oxidant inhibition of epithelial active sodium transport

The purpose of this study was to quantify the effects of extracellularly generated partially reduced oxygen species on active sodium (NA⁺) transport across the ventral toad skin, a well-studied epithelium. Sections of skin from decapitated toads were mounted in an Ussing chamber, bathed on both sides with electrolyte solution containing 500 μM xanthine and bubbled continuously with room air. The tissues were short-circuited, and short circuit current (Isc) and tissue resistance (R_t were monitored continuously with an automatic voltage clamp apparatus. Fifteen mU/ml of xanthine oxidase (XO), either purchased from Calbiochem or purified from cream, were instilled in either the apical (mucosal) or basolateral (serosal) baths at t = 0 and T = 10 min. Hydrogen peroxide (H₂O₂) concentrations increased to 200 μM within the first 20 min and then decreased, reaching a value of 40 μM by 60 min. Mean [H₂O₂] was 90 μM. Instillation of XO in the apical bath resulted in a large decrease in Isc and an increase in R_t, their values being 43% and 160% of their corresponding controls 85 min after the first instillation. Addition of superoxide dismutase and catalase completely prevented these changes. Instillation of XO in the basolateral bath had no effect. Similar physiological responses were obtained using the Calbiochem XO or the purified XO, which contained no measurable protease activity. It was concluded that extracellularly generated partially reduced oxygen species may interfere with active Na⁺ transport by possibly damaging apical Na⁺ channel proteins.     

Vanadate-stimulated oxidation of NAD(P)H

Vanadate stimulates the oxidation of NAD(P)H by biological membranes because such membranes contain NAD(P)H oxidases which are capable of reducing dioxygen to O₂⁻ and because vanadate catalyzes the oxidation of NAD(P)H by O₂⁻, by a free radical chain mechanism. Dihydropyridines, such as reduced nicotinamide mononucleotide (NMNH), which are not substrates for membrane-associated NAD(P)H oxidases, are not oxidized by membranes plus vanadate unless NAD(P)H is present to serve as a source of O₂⁻. When [NMNH] greatly exceeds [NAD(P)H], in such reaction mixtures, one can observe the oxidation of many molecules of NMNH per NAD(P)H consumed. This reflects the chain length of the free radical chain mechanism. We have discussed the mechanism and significance of this process and have tried to clarify the pertinent but confusing literature.     

Chemiluminescent oxidation of ribose catalyzed by horseradish peroxidase in presence of hydrogen peroxide

The reaction of ribose with horseradish peroxidase in the presence of H₂O₂ is accompanied by light emission. The detection of horseradish peroxidase Compound II (FeO²⁺) indicates that the enzyme participates in a normal peroxidatic cycle. Hydrogen peroxide converts horseradish peroxidase into Compound I (FeO³⁺) which in turn is converted into Compound II by abstracting a hydrogen atom from ribose forming a ribosyl radical. In aerated solutions oxygen rapidly adds to the ribosyl radical. Based on the spectral characteristics and the enhancement of the chemiluminescence by chlorophyll-a, xanthene dyes, D₂O and DABCO, it is suggested that the excited species, apparently triplet carbonyls and ¹O₂, are formed from the bimolecular decay of the peroxyl radicals via the Russell mechanism.     

Regulation of UDP-Galactose:Ceramide Galactosyltransferase and UDP-Glucose:Ceramide Glucosyltransferase After Crush and Transection Nerve Injury

The enzyme activities of ceramide galactosyltransferase and ceramide glucosyltransferase were assayed as a function of time (0, 1, 2, 4, 7, 14, 21, 28, and 35 days) after crush injury or permanent transection of the adult rat sciatic nerve. These experimental models of neuropathy are characterized by the presence and absence of axonal regeneration and subsequent myelin assembly. Within the first 4 days after both injuries, a 50% reduction of ceramide galactosyltransferase-specific activity was observed compared to values found in the normal adult nerve. This activity remained unchanged at 7 days after injury; however, by 14 days the ceramide galactosyltransferase activity diverged in the two models. The activity increased in the crushed nerve and reached control values by 21 days, whereas a further decrease was observed in the transected nerve such that the activity was nearly immeasurable by 35 days. In contrast, the ceramide glucosyltransferase activity showed a rapid increase between 1 and 4 days, followed by a plateau that was 3.4-fold greater than that in the normal adult nerve, which persisted throughout the observation period in both the crush and transection models. [3H]Galactose precursor incorporation studies at 7, 14, 21, and 35 days after injury confirmed the previously observed shift in biosynthesis from the galactocerebrosides during myelin assembly in the crush model to the glucocerebrosides and oligohexosylceramide homologues in the absence of myelin assembly in the transection model. The transected nerves were characterized by a peak of biosynthesis of the glucocerebrosides at 14 days. Of particular interest is the biosynthesis of the glucocerebrosides and the oligohexosylceramides at 7 and 14 days after crush injury.(ABSTRACT TRUNCATED AT 250 WORDS)     

The Influence of water salinity on the free amino acid concentration in muscle and hepatopancreas of adult shrimps, Penaeus japonicus

Variations of the total free amino acid (FAA) pool and the content of specific amino acids have been measured in the muscle and hepatopancreas of adult shrimps, Penaeus japonicus, acclimatized at five water salinities: 38, 32, 26, 20 and 14%‰ The FAA content is always higher in muscle than in hepatopancreas at all tested salinites. On the other hand, the hepatopancreas exhibits the highest concentrations of essential amino acids. Two steps in the evolution of FAA content can be observed, the first one regarding decrease in salinity from 38 to 20%‰ and the second one, when salinity goes below 20%_°. The first step can be characterized by a 16% decrease of total FAA content in the muscle and a 36% increase in the hepatopancreas. In muscle, the variations are mainly due to changes in non-essential FAA content, whereas in the hepatopancreas, they are linked to variations in essential FAA content. The other step is characterized by a drastic increase in moisture and decrease in FAA content in both studied organs when water salinity is 14%‰ The total FAA content is about 40% lower in shrimps at 14%_° compared to 38%‰ seawater salinity. During adaptation, the FAA pool (mainly NEFAAs) of muscle seems to be directly related to osmoregulation, whereas in the hepatopancreas, its evolution seems to be linked with energy expenditure and protein synthesis. The results are evaluated in order to elucidate the role of FAA in intracellular osmoregulation and in relation to animal ecology.     

Age-related effect induced by oxidative stress on the cerebral glutathione system

In the forebrain from male Wistar rats aged 5, 15 and 25 months, age-related putative alterations in the glutathione system (reduced and oxidized glutathione; redox index) were chronically induced by the administration in drinking water of free radical generators (hydrogen peroxide, ferrous chloride) or of inhibitors of endogenous free radical defenses (diethyl-dithio-carbamate, an inhibitor of superoxide dismutase activity). In hydrogen peroxide administered rats, both reduced glutathione and the cerebral glutathione redox index markedly declined as a function of aging, whereas oxidized glutathione consistently increased. In contrast, chronic iron intake failed to modify the reduced glutathione in forebrain from the rats of the different ages tested, whereas the oxidized glutathione was increased in the older brains. The chronic intake of diethyl-dithio-carbamate enhanced the concentrations of reduced glutathione in the forebrains from the rats of the different ages tested, the oxidized glutathione being unchanged. In 15-month-old rats submitted to chronic oxidative stress, ergot alkaloids (and particularly dihydroergocriptine) interfered with cerebral glutathione system, while papaverine was always ineffective. The comprehensive analysis of the data indicates that: (a) both the type of oxidative stress and the age of the animals modulate the cerebral responsiveness to the putative modifiers in the level of tissue free radicals; (b) aging magnifies the cerebral alterations induced by oxidative stress; the (c) cerebral glutathione system may be modified by metabolic rather than by circulatory interferences; (d) a balance between the various cerebral antioxidant defenses is present, the perturbation of an antioxidant system resulting in the compensatory modified activity of component(s) of another system.