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101.
Catherine Rice-evans David Leake K. Richard Bruckdorfer Anthony T. Diplock 《Free radical research》1996,25(4):285-311
The purpose of this review is to bring together the different approaches for studying the oxidation of low density lipoproteins and try to identify some critical factors which will permit greater comparability between laboratories. These issues are discussed both in terms of the variety of exogenous mediators of oxidation applied (transition metal ions, haem proteins, azo initiators, peroxynitrite, cells etc.) and their raisons d'etre, as well as the methodologies (formation of conjugated dienes, hydroperoxides, decomposition products of lipid peroxidation, altered surface charge, macrophage uptake) applicable to the different stages of the oxidation and the factors underlying their accurate execution and interpretation. 相似文献
102.
103.
Compartmentation and flux characteristics of nitrate in spruce 总被引:8,自引:0,他引:8
The radiotracer13N was used to undertake compartmental analyses for NO
3
–
in intact non-mycorrhizal roots ofPicea glauca (Moench) Voss. seedlings. Three compartments were defined, with half-lives of exchange of 2.5 s, 20 s, and 7 min. These were identified as representing surface adsorption, apparent free space, and cytoplasm, respectively. Influx, efflux, and net flux as well as cytoplasmic and apparent-free-space nitrate concentrations were estimated for three different concentration regimes of external nitrate. After exposure to external NO
3
–
for 3 d, influx was calculated to be 0.09 mol·g–1·h–1 (at 10 M [NO
3
–
]o), 0.5mol·g–1·h–1 (at 100 M [NO
inf3
sup–
]o), and 1.2 mol · g–1· h–1 (at 1.5 mM [NO
3
–
]o). Efflux increased with increasing [NO
3
–
]o, constituting 4% of influx at 10 M, 6% at 100 M, and 21% at 1.5 mM. Cytoplasmic [NO
3
–
] was estimated to be 0.3 mM at 10 uM [NO
3
–
]o, 2mM at 100 M [NO
3
–
]o, and 4mM at 1.5 mM [NO
3
–
]o, while free-space [NO
3
–
] was 16 M, 173 M, and 2.2 mM, respectively. A series of experiments was carried out to confirm the identity of the compartments resolved by efflux analysis. Pretreatment at high temperature or application of 2-chloro-ethanol, sodium dodecyl sulphate or hydrogen peroxide made it possible to distinguish the metabolic (cytoplasmic) phase from the remaining two (physical) phases. Likewise, varying [Pi] of the medium altered efflux and thereby [NO
3
–
]cyt, but did not affect [NO
3
–
]free space.Abbreviations and Symbols [NO
3
–
]cyt
cytoplasmic NO
3
–
concentration
- [NO
3
–
]free space
apparent-free-space NO
3
–
concentration
- [NO
3
–
]o
concentration of NO
3
–
in the external solution
-
NO
3
–
flux
- co
efflux from the cytoplasm
- oc
influx to the cytoplasm
- net
net flux
- xylem
flux to the xylem
- red/vac
combined flux to reduction and the vacuole
The research was supported by a Natural Sciences and Engineering Research Council, Canada, grant to Dr. A.D.M. Glass and by a University of British Columbia Graduate Fellowship to Herbert J. Kronzucker. Our thanks go to Dr. M. Adam and Mr. P. Culbert at the particle accelerator facility TRIUMF on the University of British Columbia Campus for providing13NO
3
–
, Drs. R.D. Guy and S. Silim for providing plant material, and Dr. M.Y. Wang, Mr. J. Mehroke and Mr. P. Poon for assistance in experiments and for helpful discussions. 相似文献
104.
Anthony L. Moore Ann L. Umbach James N. Siedow 《Journal of bioenergetics and biomembranes》1995,27(4):367-377
A major characteristic of plant mitochondria is the presence of a cyanide-insensitive alternative oxidase which catalyzes the reduction of oxygen to water. Current information on the properties of the oxidase is reviewed. Conserved amino acid motifs have been identified which suggest the presence of a hydroxo-bridged di-iron center in the active site of the alternative oxidase. On the basis of sequence comparison with other di-iron center proteins, a structural model for the active site of the alternative oxidase has been developed that has strong similarity to that of methane monoxygenase. Evidence is presented to suggest that the alternative oxidase of plant mitochondria is the newest member of the class II group of di-iron center proteins. 相似文献
105.
It is widely held that there was a phosphate compound in prebiotic chemistry that played the role of adenosine triphosphate and that the first living organisms had ribose-phosphate in the backbone of their genetic material. However, there are no known efficient prebiotic synthesis of high-energy phosphates or phosphate esters. We review the occurrence of phosphates in Nature, the efficiency of the volcanic synthesis of P4O10, the efficiency of polyphosphate synthesis by heating phosphate minerals under geological conditions, and the use of high-energy organic compounds such as cyanamide or hydrogen cyanide. These are shown to be inefficient processes especially when the hydrolysis of the polyphosphates is taken into account. For example, if a whole atmosphere of methane or carbon monoxide were converted to cyanide which somehow synthesized polyphosphates quantitatively, the polyphosphate concentration in the ocean would still have been insignificant. We also attempted to find more efficient high-energy polymerizing agents by spark discharge syntheses, but without success. There may still be undiscovered robust prebiotic syntheses of polyphosphates, or mechanisms for concentrating them, but we conclude that phosphate esters may not have been constituents of the first genetic material. Phosphoanhydrides are also unlikely as prebiotic energy sources.
Correspondence to: S.L. Miller 相似文献
106.
José A. A. Sant''Ana Pereira Arnold De Haan Andy Wessels Antoon F. M. Moorman Anthony J. Sargeant 《The Histochemical journal》1995,27(9):715-722
Summary In the present study we report a novel histochemical method which, by sequential pre-incubations in alkaline and acidic media,
selectively differentiates muscle fibres expressing myosin heavy chain IIX, on the basis of a specific profile for myofibrillar
actomyosin ATPase (mATPase) activity. The enzyme reactions were tested for specificity by means of anti-myosin heavy chain
monoclonal antibodies, which were characterized on Western blots of muscle homogenates. Enzyme histochemical reactions with
the traditional pH buffers were compared to those of the new method and, in conjunction with the immunoreactions, used to
confirm the relationship between MyHC expression and the distinct profiles for mATPase. Imrnunohistochemical reactions demonstrated
that the new method only differentiates those fibres expressing myosin heavy chain IIX. The method revealed a continuum in
which the intermediate staining intensities corresponded to hybrid fibres expressing myosin heavy chain IIX in combination
with either the IIA or IIB forms. Quantitative histochemistry and immunohistochemistry (by image analysis), used to examine
the relationship between staining intensities for mATPase and amounts of myosin heavy chain IIX expression, revealed that
the new method discriminates well between hybrid fibres expressing variable amounts of the IIX isoform (r2 = 0.93). 相似文献
107.
Nathaniel M. Bachrach Wilmot B. Valhmu Enrico Stazzone Anthony Ratcliffe W. Michael Lai Van C. Mow 《Journal of biomechanics》1995,28(12):1561-1569
Explant loading experiments were conducted to investigate the effect of load duration on proteoglycan synthesis. A compressive load of 0.1 MPa applied for 10 min was found to stimulate proteoglycan synthesis, while the same load applied for 20 h suppressed synthesis. This bimodal response suggests that the cells are responding to different mechanical stimuli as time progresses. A theoretical model has therefore been developed to describe the mechanical environment perceived by cells within soft hydrated tissues (e.g. articular cartilage) while the tissue is being loaded. The cells are modeled, using the biphasic theory, as fluid-solid inclusions embedded in and attached to a biphasic extracellular matrix of distinct material properties. A method of solution is developed which is valid for any axisymmetric loading configuration, provided that the cell radius, a, is small relative to the tissue height, h (i.e. h/a 1). A closed-form analytical solution for this inclusion problem is then presented for the confined compression configuration. Results from this model show that the mechanical environment in and around the cells is time dependent and inhomogeneous, and can be significantly influenced by differences in properties between the cell and the extracellular matrix. 相似文献
108.
Abstract: Mice infected with the LP-BM5 murine leukemia virus mixture develop severe immunosuppression and an encephalopathy characterized by spatial learning deficits. Twelve weeks after infection of C57BL/6J mice with LP-BM5, significant (50–60%) reductions in Met-enkephalin and substance P levels were observed in the striatum, whereas somatostatin levels were unchanged. In addition, a 39% decrease in hypothalamic substance P concentrations was observed, with no alteration in Met-enkephalin levels. The apparent selectivity of the decrease in neuropeptide concentrations indicates that a functional alteration of the primary striatal efferent neurons occurs in this infection, which may contribute to the impairment of spatial learning observed in these mice. Moreover, this decrease in striatal neuropeptide levels is similar to the neuropathological changes in basal ganglia observed in HIV-infected individuals and is consistent with previous studies suggesting that the LP-BM5-infected mouse may serve as a useful model of AIDS dementia. 相似文献
109.
In plasmid pTF-FC2, three small open reading frames (ORFs) are situated between the repB (primase) gene and the repA (helicase) gene of its IncQ-type replicon. Disruption of each of the three ORFs followed by tests for plasmid stability and host cell growth indicated that the ORFs encoded a poison–antidote plasmid stability system. The three genes were named pasA , pasB and pasC (plasmid addiction system), in which PasA is the antidote, PasB the toxin and PasC a protein that appears to enhance the ability of the antidote to neutralize the toxin. Disruption of the pasA gene resulted in two different spontaneous deletions, which inactivated the stability system but did not alter the host range or plasmid copy number. This indicated that the three small ORFs were not involved in plasmid replication. When placed behind a tac promoter, induction of pasB was found to be highly lethal to host cells, which suggests that the Pas system acts by killing plasmid-free host cells rather than by retarding the growth of plasmid-free segregants, as occurs in the ParD system of R1. In spite of this, the presence of the Pas poison–antidote system resulted in a relatively modest threefold stabilization of the pTF-FC2 host replicon and a similar increase in the stabilization of an unstable heterologous R1 plasmid replicon. The Pas system is a poison–antidote plasmid stability module, which appears to have become integrated within the pTF-FC2 replicon module. 相似文献
110.
The ability of type II DNA topoisomerases to perturb the equilibrium distributions of DNA topoisomers is a consequence of their ability to hydrolyse ATP. A sliding mechanism of topoisomerase action has been proposed to account for this phenomenon. 相似文献