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21.
Beneficial interaction between photosynthesis and respiration in mesophyll protoplasts of pea during short light-dark cycles 总被引:1,自引:0,他引:1
The respiratory uptake or photosynthetic evolution of oxygen by mesophyll protoplasts of pea ( Pisum sativum L. cv. Arkel) were monitored during successive short. (3–5 min) cycles of darkness and illumination. The rate of respiration was nearly doubled after 3–4 short periods of illumination while there was a 15–20% enhancement in photosynthesis with cycles of illumination and darkness preceding illumination. Such interaction between photosynthesis and respiration was statistically significant when bicarbonate was present in the reaction medium. The inhibitors of photosynthesis [3(3,4–dichlorophenyl)-l,l-dimethylurea (DCMU), glyceraldehyde] decreased respiration after periods of illumination, whereas inhibitors of respiratory electron transport (Rotenone, antimycin A, NaN3 ) suppressed photosynthesis, as well. We suggest that a rapid beneficial interaction exists between photosynthesis and respiration in protoplasts, even during short cycles of light and darkness. 相似文献
22.
The level of α-mannanase in mixed fungal culture of Trichoderma reesei, D1-6, and Aspergillus wentii, Pt 2804, affects the
extracellular activities of cellulase. The endoglucanase component of the cellulase system is a glycoprotein having mannose
and other sugars and sugaramines in its glycan moiety. Its activity is inhibited by α-mannanase. The inactivation of endoglucanase
by α-mannanase can be prevented by galactose. 相似文献
23.
Abstract: Characteristics of the transport of the nitric oxide synthase substrate l -arginine and its inhibitor, N G -nitro- l -arginine ( l -NOARG), into rat cerebellar synaptosomes were studied. Uptake of both l -arginine and l -NOARG was linear with increasing amount of protein (up to 40 µg) and time of incubation (up to 5 min) at 37°C. Uptake of both compounds reached a steady state by 20 min. Maximal uptake of l -NOARG (650 pmol/mg of protein) was three to four times higher than that of l -arginine (170 pmol/mg of protein). l -NOARG uptake showed biphasic kinetics ( K m 1 = 0.72 m M , V max 1 = 0.98 nmol/min/mg of protein; K m 2 = 2.57 m M , V max 2 = 16.25 nmol/min/mg of protein). l -Arginine uptake was monophasic with a K m of 106 µ M and a V max of 0.33 nmol/min/mg of protein. l -NOARG uptake was selectively inhibited by l -NOARG, N G -nitro- l -arginine methyl ester, and branched-chain and aromatic amino acids. l -Alanine and l -serine also inhibited l -NOARG uptake but with less potency. Uptake of l -arginine was selectively inhibited by N G -monomethyl- l -arginine acetate and basic amino acids. These studies suggest that in rat cerebellar synaptosomes, l -NOARG is transported by the neutral amino acid carrier systems T and L with high affinity, whereas l -arginine is transported by the basic amino acid carrier system y+ with high affinity. These data indicate that the concentration of competing amino acids is an important factor in determining the rates of uptake of l -NOARG and l -arginine into synaptosomes and, in this way, may control the activity of nitric oxide synthase. 相似文献
24.
Viral replication is required for induction of ocular immunopathology by herpes simplex virus. 总被引:7,自引:1,他引:6 下载免费PDF全文
J S Babu J Thomas S Kanangat L A Morrison D M Knipe B T Rouse 《Journal of virology》1996,70(1):101-107
Corneal infection of BALB/c mice with herpes simplex virus type 1 results in a chronic inflammatory response in the stroma termed herpetic stromal keratitis (HSK). This disease is considered to be immunopathological and mediated primarily by CD4+ T cells of the type 1 cytokine profile. However, the nature of the antigens, virus or host derived, which drive the inflammatory response remains in doubt. In this study, the relevance of infection with replicating virus for the subsequent development of HSK was evaluated with immunocompetent mice as well as with SCID mice reconstituted with herpes simplex virus-immune CD4+ T cells. In the corneas of immunocompetent mice, infectious virus, viral antigen, and mRNA expression were detectable for only a brief period of time (< or = 7 days postinfection), and all were undetectable by the time clinical lesions were evident (10 to 15 days). Viral replication, however, was necessary for the development of HSK in both models, since infection with UV-inactivated virus or with mutant viruses which were incapable of multiple rounds of replication in vivo failed to induce HSK. The inactivated and mutant viral preparations did, however, stimulate T-cell immune responses in immunocompetent mice. The results are discussed in terms of possible involvement of host antigens exposed in response to transient progeny virion replication in the immune-privileged cornea. 相似文献
25.
Three to four families of nuclear genes encode different isoforms of phosphoenolpyruvate (PEP) carboxylase (PEPC): C4-specific, C3 or etiolated, CAM and root forms. C4 leaf PEPC is encoded by a single gene (ppc) in sorghum and maize, but multiple genes in the C4-dicot Flaveria trinervia. Selective expression of ppc in only C4-mesophyll cells is proposed to be due to nuclear factors, DNA methylation and a distinct gene promoter. Deduced amino acid sequences of C4-PEPC pinpoint the phosphorylatable serine near the N-terminus, C4-specific valine and serine residues near the C-terminus, conserved cysteine, lysine and histidine residues and PEP binding/catalytic sites. During the PEPC reaction, PEP and bicarbonate are first converted into carboxyphosphate and the enolate of pyruvate. Carboxyphosphate decomposes within the active site into Pi and CO2, the latter combining with the enolate to form oxalacetate. Besides carboxylation, PEPC catalyzes a HCO3
--dependent hydrolysis of PEP to yield pyruvate and Pi. Post-translational regulation of PEPC occurs by a phosphorylation/dephosphorylation cascade in vivo and by reversible enzyme oligomerization in vitro. The interrelation between phosphorylation and oligomerization of the enzyme is not clear. PEPC-protein kinase (PEPC-PK), the enzyme responsible for phosphorylation of PEPC, has been studied extensively while only limited information is available on the protein phosphatase 2A capable of dephosphorylating PEPC. The C4
ppc was cloned and expressed in Escherichia coli as well as tobacco. The transformed E. coli produced a functional/phosphorylatable C4 PEPC and the transgenic tobacco plants expressed both C3 and C4 isoforms. Site-directed mutagenesis of ppc indicates the importance of His138, His579 and Arg587 in catalysis and/or substrate-binding by the E. coli enzyme, Ser8 in the regulation of sorghum PEPC. Important areas for further research on C4 PEPC are: mechanism of transduction of light signal during photoactivation of PEPC-PK and PEPC in leaves, extensive use of site-directed mutagenesis to precisely identify other key amino acid residues, changes in quarternary structure of PEPC in vivo, a high-resolution crystal structure, and hormonal regulation of PEPC expression.Abbreviations OAA
oxalacetate
- PEP
phosphoenolpyruvate
- PEPC
PEP carboxylase
- PEPC-PK
PEPC-protein kinase
- PPDK
pyruvate, orthophosphate dikinase
- Rubisco
ribulose 1,5-bis-phosphate carboxylase/oxygenase
- CAM
Crassulacean acid metabolism 相似文献
26.
D. Sudha Sundari K. Saradadevi A. S. Raghavendra 《Journal of plant biochemistry and biotechnology.》1994,3(2):137-140
When spinach chloroplast membranes were exposed to osmotic stress in vitro, by incubation in 1.0 M sorbitol + 10 mM MgCl2 their oxygen evolving system was suppressed. The possible reasons for such inactivation of PS II mediated oxygen evolution were examined. There were conformational changes in the chloroplast membranes, as indicated by their absorption spectra. The pattern of sensitivity to DCMU was not altered. The sensitivity of PS II to water stress remained, even after a pre-wash treatment with NaCI (which removed 18 and 24 kD proteins) but not when the thylakoids were pretreated with NH20H or CaCl2 (removed manganese and 33 kD). The manganese content of thylakoid membranes was markedly reduced under osmotic stress in presence of magnesium. We suggest that exposure of chloroplasts to 1.0 M sorbitol in presence of Mg2+ released manganese from thylakoid membranes, thereby leading to a suppression in oxygen evolution. 相似文献
27.
Astrocytes, neuronal perikarya and synaptosomes were prepared from rat cerebellum. Kinetics of high and low affinity uptake systems of glutamate and aspartate, nominal rates of14CO2 production from [U–14C]glutamate, [U–14C]aspartate and [1–14C]glutamate and activities of enzymes of glutamate metabolism were studied in these preparations. The rate of uptake and the nomial rate of production of14CO2 from these amino acids was higher in the astroglia than neuronal perikarya and synaptosomes. Activities of glutamine synthetase and glutamate dehydrogenase were higher in astrocytes than in neuronal perikarya and synaptosomes. Activities of glutaminase and glutamic acid decarboxylase were observed to be highest in neuronal perikarya and synaptosomes respectively. These results are in agreement with the postulates of theory of metabolic compartmentation of glutamate while others (presence of glutaminase in astrocytes and glutamine synthetase in synaptosomes) are not. Results of this study also indicated that (i) at high extracellular concentrations, glutamate/aspartate uptake may be predominantly into astrocytes while at low extracellular concentrations, it would be into neurons (ii) production of -ketoglutarate from glutamate is chiefly by way of transamination but not by oxidative deamination in these three preparations and (iii) there are topographical differences glutamate metabolism within the neurons. 相似文献
28.
29.
G. Phanendra Babu 《Biological cybernetics》1995,73(4):367-374
Clustering techniques are used to discover structure in data by optimizing a defined criterion function. Most of these methods
assume that the data are stationary, and these techniques are based on gradient descent which converge to a locally optimal
clustering. There are many potential applications that require clustering to be performed in non-stationary temporal environments.
In this paper, we investigate the applicability of a clan-based evolutionary optimization method for clustering data in non-stationary
environments. Due to the stochastic nature of the technique, the problem of becoming entrapped in local optima is avoided,
and the method can converge to (nearly) optimal clusters. Different cases are considered in the experiments, and the results
demonstrate the efficacy of the evolutionary approach for clustering time-varying data.
Received: 7 September 1994/Accepted in revised form: 28 March 1995 相似文献
30.
Summary Glutamate (Glu) the major amino acid in mammalian brain and most dietary proteins possesses neurotransmitter as well as neurotoxic properties. We administered monosodium glutamate (MSG) 4 mg/g bwt, sc on postnatal day (PND) 1 through 10 to rats on alternate days or daily and sacrificed them on PND 45 or PND 90 respectively. The activities of glutamate dehydrogenase and aminotransferases were evaluated in the circumventricular organs of brain. Results show that neonatal MSG produces alterations in glutamate metabolism in blood-brain-barrier deficient regions. 相似文献