共查询到20条相似文献,搜索用时 31 毫秒
1.
Boyd R. Switzer George K. Summer 《In vitro cellular & developmental biology. Plant》1973,9(3):160-166
Summary In human diploid skin fibroblasts in culture we have shown that nonhydroxylated collagen precursors remain in the cell when
proline hydroxylation is inhibited by α, α′-dipyridyl, a chelator of ferrous ions. The inhibition of proline hydroxylation
is reversed by addition of fresh medium containing 50 μg per ml of sodium ascorbate, whereupon nonhydroxylated collagen precursors
are hydroxylated within the cell and extruded into the medium. Extrusion of collagen already formed within the cell is not
appreciably affected by α, α′-dipyridyl inhibition. Under normal conditions collagen is released from the monolayer into the
medium within 3 hr of a pulse ofL[14C]proline. In the presence of α, α′-dipyridyl, about 35% of theL[14C]proline incorporated into protein is released into the medium within 8 hr as a proline-rich, hydroxyproline-deficient protein;
at the same time, approximately 15% of the protein-boundl-[14C]proline remains in the cell for as long as 12 hr. When proline hydroxylation is restored after 2 and 12 hr of α, α′-dipyridyl
inhibition, approximately the same amount of hydroxyproline is formed after each time interval in the monolayer. Therefore,
nonhydroxylated collagen precursors retained in the cell are not appreciably degraded during at least 12 hr of inhibition
by α, α′-dipyridyl and are extruded into the medium only upon restoration of hydroxylation.
This work was supported in part by a grant from the Easter Seal Research Foundation, and by Project 236, Health Services and
Mental Health Administration, Department of Health, Education and Welfare, Grant HD-03110 from the National Institute of Child
Health and Human Development, an American Cancer Society Institutional Grant (1N 15-J), a General Research Support Award (5-S01-FR-05406)
from the National Institutes of Health, a University Research Council Grant, a National Science Foundation Equipment Grant
(GB-4577), and a Research Career Development Award (5-K3-AM-5058) from the National Institute of Arthritis and Metabolic Disease
(G.K.S.). 相似文献
2.
3.
Schreiber SJ 《Journal of mathematical biology》2001,42(3):239-260
A class of truncated unimodal discrete-time single species models for which low or high densities result in extinction in
the following generation are considered. A classification of the dynamics of these maps into five types is proven: (i) extinction
in finite time for all initial densities, (ii) semistability in which all orbits tend toward the origin or a semi-stable fixed
point, (iii) bistability for which the origin and an interval bounded away from the origin are attracting, (iv) chaotic semistability
in which there is an interval of chaotic dynamics whose compliment lies in the origin’s basin of attraction and (v) essential
extinction in which almost every (but not every) initial population density leads to extinction in finite time. Applying these
results to the Logistic, Ricker and generalized Beverton-Holt maps with constant harvesting rates, two birfurcations are shown
to lead to sudden population disappearances: a saddle node bifurcation corresponding to a transition from bistability to extinction
and a chaotic blue sky catastrophe corresponding to a transition from bistability to essential extinction.
Received: 14 February 2000 / Revised version: 15 August 2000 / Published online: 16 February 2001 相似文献
4.
Pontoni G Rotondo F Spagnuolo G Aurino MT Cartenì-Farina M Zappia V Lama G 《Amino acids》2000,19(2):469-476
Summary. Proton Nuclear Magnetic Resonance (NMR) Spectroscopy of urine (as well as of other biological fluids) is a very powerful
technique enabling multi-component analysis useful in both diagnosis and follow-up of a wide range of inherited metabolic
diseases. Among these pathologies, cystinuria is characterised by accumulation in urine of four dibasic amino acids, namely
lysine, arginine, ornithine and cystine; the last one, being only slightly water soluble, generates urolithiasis. The mentioned
aminoacids can be detected in the urine NMR spectrum of cystinuric patients, the most abundant being the lysine (5 mM and
over are often detected), whose typical signals become very high; arginine and ornithine are also usually detectable, although
pathologic concentrations are lower (usually below 2 mM).
The proposed NMR technique is also suitable in monitoring the therapy with α-mercaptopropionylglycine (MPG), providing quantitation
of several metabolites of interest in the follow-up of the pathology, like cystine, creatinine and citrate.
Received May 9, 1999; Accepted September 26, 1999 相似文献
5.
Summary. The accumulation of oxidized proteins is known to be linked to some severe neurodegenerative diseases like Alzheimer’s, Parkinson’s
and Huntington’s disease. Furthermore, the aging process is also accompanied by an ongoing aggregation of misfolded and damaged
proteins. Therefore, mammalian cells have developed potent degradation systems, which selectively degrade damaged and misfolded
proteins. The proteasomal system is largely responsible for the removal of oxidatively damaged proteins form the cellular
environment. Not only cytosolic proteins are prone to oxidative stress, also nuclear proteins are readily oxidized. The nuclear
proteasomal system is responsible for the degradation of these proteins. This review is focused on the specific degradation
of oxidized nuclear proteins, the role of the proteasome in this process and the regulation of the nuclear proteasomal system
under oxidative conditions. 相似文献
6.
Plants acclimate to changes in light quantity by altering leaf-cell development and the accumulation of chloroplast components,
such that light absorption is favoured under limiting illumination, and light utilisation under non-limiting conditions. Previous
evidence suggests an involvement of a high-light photosynthetic redox signal in the down-regulation of the accumulation of
the light-harvesting complexes of photosystem II (Lhcb) and the expression of the Lhcb genes, and of a blue-light signal in the control of leaf development and in the increase in photosynthetic capacity, as affected
by the accumulation of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco). We examined the internal anatomy of leaves,
the ultrastructure of chloroplasts and accumulation of light-harvesting complexes and Rubisco in wild-type Arabidopsis thaliana (L.) Heynh. and in mutants in each of the three known blue-light photoreceptors, cryptochrome 1, cryptochrome 2 and phototropin,
as well as a mutant in both cryptochromes. Our results indicate an extensive capacity of the Arabidopsis mesophyll cells to adapt to high light fluence rate with an increase in palisade elongation. Under high light, chloroplasts
showed increased starch accumulation and reductions in the amount of granal thylakoids per chloroplast, in the proportion
of chlorophyll b relative to chlorophyll a, and in the accumulation of the major Lhcb polypeptides. The responses were similar
for all four mutants, with respect to their wild types. The results are consistent with either a complete redundancy in function
between cryptochromes and phototropin, or their absence of involvement in the light-quantity responses tested. We observed
minimal effects of light quantity on Rubisco accumulation over the range of fluence rates used, and conclude that elongation
of palisade mesophyll cells and accumulation of Rubisco are controlled separately. This indicates that light acclimation must
be the result of a number of individual elementary responses. Quantitative differences in the acclimatory responses were observed
between the Landsberg erecta and Columbia wild-type ecotypes used.
Received: 4 April 2000 / Accepted: 14 July 2000 相似文献
7.
Geranylhydroquinone 3′′-hydroxylase, a cytochrome P-450 monooxygenase from Lithospermum erythrorhizon cell suspension cultures 总被引:2,自引:0,他引:2
Geranylhydroquinone 3′′-hydroxylase, which is likely to be involved in shikonin and dihydroechinofuran biosynthesis, was
identified in cell suspension cultures of Lithospermum erythrorhizon Sieb. et Zucc. (Boraginaceae). The enzyme hydroxylates the isoprenoid side chain of geranylhydroquinone (GHQ), a known precursor
of shikonin. Proton/proton correlation spectroscopic and proton/proton long-range correlation spectroscopic studies confirmed
that hydroxylation takes place specifically at position 3′′, i.e. at the methyl group involved in the cyclization reaction.
The enzyme is membrane-bound and was found in the microsomal fraction. It requires NADPH and molecular oxygen as cofactors,
and is inhibited by cytochrome P-450 inhibitors such as cytochrome c and CO. The inhibitory effect of CO is reversed by illumination.
These data suggest that the enzyme is a cytochrome P-450-dependent monooxygenase. The optimum pH of GHQ 3′′-hydroxylase is
7.4, and the apparent K
m value for GHQ is 1.5 μM. The reaction velocity obtained with 3-geranyl-4-hydroxybenzoic acid was more than 100 times lower
than that obtained with geranylhydroquinone.
Received: 20 March 1999 / Accepted: 20 July 1999 相似文献
8.
Summary. Mammalian hexokinase (HXK) is found at the outer mitochondrial membrane, exposed to mitochondrial oxygen- and nitrogen-radicals.
Given the important role of this enzyme in metabolic pathways and diseases, the effect of S-nitrosoglutathione (GSNO) on HXK A structure and activity was studied. To focus on the catalytic domain, yeast HXK A was
used because it has a significant homology to the mammalian domain that contains both the regulatory and catalytic sites.
Biologically relevant [GSNO]/[HXK] caused a significant decrease in Vmax with glucose (but not with fructose), along with oxidation of 5 Met and nitration of 4 Tyr. Preincubation of HXK with glucose
abrogated the effect of GSNO whereas fructose was ineffective. These results are interpreted by considering the tight binding
of glucose to the enzyme as opposed to that of fructose. The segment comprised from amino acids 304 to 306 contained the most
modifications. Given that this sequence is highly conserved in HXK from various species, a decline in activity is expected
when a high-affinity substrate is presented.
Considering that changes in primary structure are envisioned at high [GSNO]/[HXK] ratios, like those present under normal
conditions, it could be hypothesized that the high concentration of hexokinase present in fast growing tumors may serve not
only to sustain high glycolysis rates, but also to minimize protein damage that might result in activity decline, compromising
energy metabolism. 相似文献
9.
Programmed cell death: similarities and differences in animals and plants. A flower paradigm 总被引:1,自引:0,他引:1
Summary. After an overview of the criteria for the definition of cell death in the animal cell and of its different types of death,
a comparative analysis of PCD in the plant cell is reported. The cytological characteristics of the plant cell undergoing
PCD are described.
The role of plant hormones and growth factors in the regulation of this event is discussed with particular emphasis on PCD
activation or prevention by polyamine treatment (doses, timing and developmental stage of the organism) in a Developmental
cell death plant model: the Nicotiana tabacum (tobacco) flower corolla. Some of the effects of polyamines might be mediated by transglutaminase catalysis. The activity
of this enzyme was examined in different parts of the corolla during its life span showing an acropetal trend parallel to
the cell death wave. The location of transglutaminase in some sub-cellular compartments suggests that it exerts different
functions in the corolla DCD. 相似文献
10.
Keck ME 《Amino acids》2006,31(3):241-250
Summary. Affective disorders tend to be chronic and life-threatening diseases: suicide is estimated to be the cause of death in 10–15%
of individuals with major depressive disorders. Major depression is one of the most prevalent and costly brain diseases with
up to 20% of the worldwide population suffering from moderate to severe forms of the disease. Only 50% of individuals with
depression show full remission in response to currently available antidepressant drug therapies which are based on serendipitous
discoveries made in the 1950s. Previously underestimated, other severe depression-associated deleterious health-related effects
have increasingly been recognized. Epidemiological studies have provided substantial evidence that patients with depression
have a 2–4-fold increased risk both of developing cardiovascular disease and of mortality after experiencing a myocardial
infarction. The majority of patients suffering from affective disorders have measurable shifts in their stress hormone regulation
as reflected by elevated secretion of central and peripheral stress hormones or by altered hormonal responses to neuroendocrine
challenge tests. In recent years, these alterations have increasingly been translated into testable hypotheses addressing
the pathogenesis of illness. Refined molecular technologies and the creation of genetically engineered mice have allowed to
specifically target individual genes involved in regulation of corticotropin releasing factor (CRF) and vasopressin (AVP)
system elements. The cumulative evidence makes a strong case implicating dysfunction of these systems in the etiology and
pathogenesis of depression and pathological anxiety. Translation of these advances into novel therapeutic strategies has already
been started. 相似文献
11.
Empirical evidence shows that childhood diseases persist in large communities whereas in smaller communities the epidemic
goes extinct (and is later reintroduced by immigration). The present paper treats a stochastic model describing the spread
of an infectious disease giving life-long immunity, in a community where individuals die and new individuals are born. The
time to extinction of the disease starting in quasi-stationarity (conditional on non-extinction) is exponentially distributed.
As the population size grows the epidemic process converges to a diffusion process. Properties of the limiting diffusion are
used to obtain an approximate expression for τ, the mean-parameter in the exponential distribution of the time to extinction
for the finite population. The expression is used to study how τ depends on the community size but also on certain properties
of the disease/community: the basic reproduction number and the means and variances of the latency period, infectious period
and life-length. Effects of introducing a vaccination program are also discussed as is the notion of the critical community
size, defined as the size which distinguishes between the two qualitatively different behaviours.
Received: 14 February 2000 / Revised version: 5 June 2000 / Published online: 24 November 2000 相似文献
12.
Nitric oxide stimulates seed germination and de-etiolation, and inhibits hypocotyl elongation, three light-inducible responses in plants 总被引:46,自引:0,他引:46
Seed germination, greening of etiolated plants and inhibition of hypocotyl elongation are stimulated by light, which is sensed
by various types of photoreceptor. Nitric oxide (NO) has proven to be a bioactive molecule, especially in mammalian cells
and, most recently, in plants. Like some phytochrome-dependent processes, many NO-mediated ones are accomplished through increases
in cGMP levels. Given these similarities, we proposed that NO could take part in light-mediated events in plants. Here we
show that NO promotes seed germination and de-etiolation, and inhibits hypocotyl and internode elongation, processes mediated
by light. Two NO donors, sodium nitroprusside (SNP) and S-nitroso-N-acetylpenicillamine induced germination of lettuce (Lactuca sativa L. cv. Grand Rapids) seeds in conditions in which this process is dependent on light (e.g. 26 °C). This was a dose-dependent
response and was arrested by addition of an NO scavenger, carboxy-PTIO. In addition, nitrite and nitrate, two NO-decomposition
products were ineffective in stimulating germination. Wheat seedlings sprayed with SNP and grown in darkness contained 30–40%
more chlorophyll than control seedlings. Nitric-oxide-mediated partial greening was increased by light pulses, wounding and
biotic stress. Arabidopsis thaliana (L.) Heynh. (ecotype Columbia) and lettuce seedlings grown in the dark had 20%-shorter hypocotyls in NO treatments than in
control ones. On the other hand, internode lengths of potato plants growing under low light intensity and sprayed with 100 μM
SNP were also 20% shorter than control ones. These results implicate NO as a stimulator molecule in plant photomorphogenesis,
either dependent on or independent of plant photoreceptors.
Received: 27 April 1999 / Accepted: 16 June 1999 相似文献
13.
Ecological interactions between species that prefer different habitat types but come into contact in edge regions at the
interfaces between habitat types are modeled via reaction-diffusion systems. The primary sort of interaction described by
the models is competition mediated by pathogen transmission. The models are somewhat novel because the spatial domains for
the variables describing the population densities of the interacting species overlap but do not coincide. Conditions implying
coexistence of the two species or the extinction of one species are derived. The conditions involve the principal eigenvalues
of elliptic operators arising from linearizations of the model system around equilibria with only one species present. The
conditions for persistence or extinction are made explicit in terms of the parameters of the system and the geometry of the
underlying spatial domains via estimates of the principal eigenvalues. The implications of the models with respect to conservation
and refuge design are discussed.
Received: 10 June 1999 / Revised version: 7 July 2000 / Published online: 20 December 2000 相似文献
14.
Taurine release modified by GABAergic agents in hippocampal slices from adult and developing mice 总被引:2,自引:0,他引:2
Summary. In order to characterize the possible regulation of taurine release by GABAergic terminals, the effects of several agonists
and antagonists of GABA receptors on the basal and K+-stimulated release of [3H]taurine were investigated in hippocampal slices from adult (3-month-old) and developing (7-day-old) mice using a superfusion
system. Taurine release was concentration-dependently potentiated by GABA, which effect was reduced by phaclofen, saclofen
and (1,2,5,6-tetrahydropyridin-4-yl)methylphosphinic acid (TPMPA) at both ages, suggesting regulation by both GABAB and GABAC receptors. The involvement of GABAA receptors could not be excluded since the antagonist bicuculline was able to affect both basal and K+-evoked taurine release. Furthermore, several GABAB receptor effectors were able to inhibit K+-stimulated taurine release in the adults, while the GABAC receptor agonists trans-4-aminocrotonic acid (TACA) and cis-4-aminocrotonic acid (CACA) potentiated this release. The potentiation
of taurine release by agents acting on the three types of GABA receptors in both adult and developing hippocampus further
indicates the involvement of transporters operating in an outward direction. This inference is corroborated by the moderate
but significant inhibition of taurine uptake by the same compounds.
Received June 28, 1999, Accepted August 31, 1999 相似文献
15.
Oshima T 《Amino acids》2007,33(2):367-372
Summary. Recent research progress on polyamines in extreme thermophiles is reviewed. Extreme thermophiles produce two types of unique
polyamines; one is longer polyamines such as caldopentamine and caldohexamine, and the other is branched polyamines such as
tetrakis(3-aminopropyl)ammonium. The protein synthesis catalyzed by a cell-free extract of Thermus thermophilus, an extreme thermophile, required the presence of a polyamine and the highest activity was found in the presence of tetrakis(3-aminopropyl)ammonium.
In vitro experiments, longer polyamines efficiently stabilized double stranded nucleic acids and a branched polyamine, tetrakis(3-aminropyl)ammonium,
stabilized stem-and-loop structures. In T. thermophilus, polyamines are synthesized from arginine by a new metabolic pathway; arginine is converted to agmatine and then agmatine
is aminopropylated to N1-aminopropylagmatine which is converted to spermidine by an enzyme coded by a gene homologous to speB (a gene for agmatinase). In this new pathway spermidine is not synthesized from putrescine. Reverse genetic studies indicated
that the unique polyamines are synthesized from spermidine. 相似文献
16.
Satu Räsänen 《Vegetation History and Archaeobotany》2001,10(4):211-218
A set of moss samples (n=58) was collected and analysed to obtain modern pollen analogues for both natural and human induced
vegetation types in northern Fennoscandia. Vegetation types with settlement, trampling and grazing were selected from the
different latitudinal forest zones (birch, pine, and mixed forest). The moss species varied between samples but the size of
the sample was kept constant. Numerical analyses such as Redundancy Analysis (RDA) indicate that in northern areas human presence
is mainly visible as increased values of Gramineae, Rumex acetosa/acetosella, R. obtusifolius, Solidago-type and Achillea-type pollen. Partial RDA further reveals that settlement is strongly correlated with high values of Rumex acetosa/acetosella, whereas trampled sites are significantly characterised by Gramineae and, to a smaller extent, Cyperaceae pollen. It is therefore
possible to distinguish the impact of different types of human activities on vegetation on the basis of the pollen spectra.
Later, these data will be used to interpret the presence, nature, and duration of human impact from fossil records from the
same area.
Received June 6, 2001 / Accepted December 12, 2001 相似文献
17.
Structural properties of proteins specific to the myelin sheath 总被引:1,自引:0,他引:1
Kursula P 《Amino acids》2008,34(2):175-185
Summary. The myelin sheath is an insulating membrane layer surrounding myelinated axons in vertebrates, which is formed when the plasma
membrane of an oligodendrocyte or a Schwann cell wraps itself around the axon. A large fraction of the total protein in this
membrane layer is comprised of only a small number of individual proteins, which have certain intriguing structural properties.
The myelin proteins are implicated in a number of neurological diseases, including, for example, autoimmune diseases and peripheral
neuropathies. In this review, the structural properties of a number of myelin-specific proteins are described.
Author’s address: Dr. Petri Kursula, Department of Biochemistry, University of Oulu, FIN-90014 Oulu, Finland 相似文献
18.
Summary. The pathogenesis of several neurodegenerative diseases, including Alzheimer’s disease, has been linked to a condition of oxidative
and nitrosative stress, arising from the imbalance between increased reactive oxygen species (ROS) and reactive nitrogen species
(RNS) production and antioxidant defences or efficiency of repair or removal systems. The effects of free radicals are expressed
by the accumulation of oxidative damage to biomolecules: nucleic acids, lipids and proteins. In this review we focused our
attention on the large body of evidence of oxidative damage to protein in Alzheimer’s disease brain and peripheral cells as
well as in their role in signalling pathways. The progress in the understanding of the molecular alterations underlying Alzheimer’s
disease will be useful in developing successful preventive and therapeutic strategies, since available drugs can only temporarily
stabilize the disease, but are not able to block the neurodegenerative process. 相似文献
19.
Summary. Increased levels in plasma homocysteine and cysteine, and more recently, decreased levels in cysteinylglycine have been indicated
as a risk factor for vascular diseases. Most assays focused their attention only on homocysteine determination and when also
other thiols were measured, analytical times drastically increased. By modifying our previous method for thiols detection,
we set up a rapid capillary electrophoresis method for the selective quantification of plasma cysteinylglycine, cutting the
analysis time of about 50%. Samples were treated with tri-n-butylphosphine as reducing agent, proteins were precipitated with
trichloroacetic acid and released thiols were successively derivatized by the selective thiol laser-induced fluorescence-labeling
agent 5-iodoacetamidofluorescein and separated by capillary electrophoresis. A baseline separation between peaks was obtained
in about 2 min using 3 mmol/L sodium phosphate/2.5 mmol/L boric acid as electrolyte solution with 75 mmol/L N-methyl-D-glucamine
at pH 11.25 in a 47 cm long capillary with a cartridge temperature of 45 °C. The method application was checked by measuring
plasma Cys-Gly levels in a group of patients affected by retinal vein occlusion (RVO), an important cause of visual loss in
the elderly. The low levels of Cys-Gly found in the RVO patients suggest that these small thiols may have importance in the
disease development.
Authors’ addresses: Dr. Angelo Zinellu, Dr. Ciriaco Carru, Department Biomedical Sciences, Chair of Clinical Biochemistry,
University of Sassari, Viale San Pietro 43/B, 07100 Sassari, Italy 相似文献
20.
Lysyl hydroxylase (LH), with three isoenzymes in vertebrates, catalyzes the formation of hydroxylysine by acting on -X-Lys-Gly- triplets in the collagenous domains of proteins of the collagen superfamily and also in -X-Lys-Ala- or -X-Lys-Ser- sequences in the telopeptides located at the ends of the polypeptide chains in some fibril-forming collagens. The hydroxylysine residues are essential for the stability of collagen crosslinks and act as carbohydrate attachment sites. The extent of lysine hydroxylation varies between collagen types, between tissues in the same collagen type and in certain diseases, suggesting that the LH isoenzymes may have different substrate specificities. We studied here the hydroxylation of synthetic peptides representing various hydroxylation sites in type I and IV collagens by purified recombinant LHs in vitro and of a recombinant full-length type I procollagen chain coexpressed with each LH in insect cells. All three LHs hydroxylated peptides representing collagenous sequences of type I and IV collagens, although with different K(m) and V(max) values. Furthermore, all three hydroxylated the collagenous domain of the coexpressed type I procollagen chain to a similar extent. None of the isoenzymes hydroxylated peptides representing the N and C telopeptides of type I collagen, but LH2, unlike the other two isoenzymes, hydroxylated the N telopeptide in the coexpressed procollagen chain. Hydroxylation of the telopeptide lysines by LH2 thus occurs only in the context of a long peptide. These data provide the first direct evidence that LH2 is a specific telopeptide hydroxylase, while all three LHs act on collagenous sequences. 相似文献