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81.
Effect of nitrogen nutrition on the carbohydrate repression of photosynthesis in leaves of Phaseolus vulgaris L. 总被引:1,自引:0,他引:1
When carbohydrates accumulate in leaves, photosynthesis is repressed. Limited nitrogen nutrition is thought to enhance this
repressing effect. However, the interaction between carbohydrate and nitrogen limitation in leaf photosynthesis has not been
examined intensively. In this study, we grew Phaseolus vulgaris L. plants at three different nitrogen levels, and examined the effects of sucrose feeding to the roots on the nitrogen content,
carbohydrate content and photosynthetic properties of the primary leaves. Nitrogen content and photosynthetic rate were lower
and the carbohydrate content was greater in plants grown with limited nitrogen than in well-fertilized plants. Sucrose feeding
to the plants increased carbohydrate content and decreased photosynthetic rate and nitrogen content. The increase in carbohydrate
content and the decreases in nitrogen content and photosynthetic rate occurred at the same time, and the negative relationship
between the carbohydrate content and photosynthetic rate did not differ among nitrogen nutrition levels. These results show
that carbohydrate accumulation in the leaves leads to a decrease in photosynthetic rate. At low nitrogen nutrition levels,
carbohydrates accumulated markedly, which accelerated this effect. It appears that the nitrogen nutrition level influences
leaf photosynthesis through changing the carbohydrate level rather than through modifying sensitivity of the leaf to the carbohydrate
level. 相似文献
82.
83.
Araya Dharmkrong-at Chusattayanond Siriphan Boonsilp Jitra Kasisit Atsadang Boonmee Saradee Warit 《Parasitology international》2010,59(4):512-516
A Thai Acanthamoeba isolate named AS recovered from a corneal scraping of a keratitis patient was genotypically determined as T4. AS trophozoites were used for studying Acanthamoeba-induced apoptosis in mouse neuroblastoma NA cells during in vitro co-cultivation. The Acanthamoeba-exposed NA cells showed signs of apoptosis including cell shrinkage, nuclear condensation and DNA fragmentation. The effect was confirmed by DNA laddering electrophoresis. Involvement of caspase enzymes and mitochondrial pro- and anti-apoptotic proteins (Bax and Bcl-2) in AS-induced apoptosis was determined. The use of Z-VAD-FMK, a pan-caspase inhibitor, significantly reduced the apoptotic effect, while Bax/Bcl-2 ratio analysis showed a significant increase in the expression of apoptotic proteins in AS-exposed NA cells. These results strongly indicated that apoptosis induced by AS trophozoites is caspase-dependent and is mediated by over-expression of pro-apoptotic proteins in the mitochondrial pathway. This is the first report on the role of Bax in mediating apoptosis induced by Acanthamoeba. 相似文献
84.
85.
The aim of the present study was to identify the enzymes in human liver catalyzing hydroxylations of bile acids. Fourteen recombinant expressed cytochrome P450 (CYP) enzymes, human liver microsomes from different donors, and selective cytochrome P450 inhibitors were used to study the hydroxylation of taurochenodeoxycholic acid and lithocholic acid. Recombinant expressed CYP3A4 was the only enzyme that was active towards these bile acids and the enzyme catalyzed an efficient 6alpha-hydroxylation of both taurochenodeoxycholic acid and lithocholic acid. The Vmax for 6alpha-hydroxylation of taurochenodeoxycholic acid by CYP3A4 was 18.2 nmol/nmol P450/min and the apparent Km was 90 microM. Cytochrome b5 was required for maximal activity. Human liver microsomes from 10 different donors, in which different P450 marker activities had been determined, were separately incubated with taurochenodeoxycholic acid and lithocholic acid. A strong correlation was found between 6alpha-hydroxylation of taurochenodeoxycholic acid, CYP3A levels (r2=0.97) and testosterone 6beta-hydroxylation (r2=0.9). There was also a strong correlation between 6alpha-hydroxylation of lithocholic acid, CYP3A levels and testosterone 6beta-hydroxylation (r2=0.7). Troleandomycin, a selective inhibitor of CYP3A enzymes, inhibited 6alpha-hydroxylation of taurochenodeoxycholic acid almost completely at a 10 microM concentration. Other inhibitors, such as alpha-naphthoflavone, sulfaphenazole and tranylcypromine had very little or no effect on the activity. The apparent Km for 6alpha-hydroxylation of taurochenodeoxycholic by human liver microsomes was high (716 microM). This might give an explanation for the limited formation of 6alpha-hydroxylated bile acids in healthy humans. From the present results, it can be concluded that CYP3A4 is active in the 6alpha-hydroxylation of both taurochenodeoxycholic acid and lithocholic acid in human liver. 相似文献
86.
87.
88.
Gamma carbonic anhydrases in plant mitochondria 总被引:2,自引:0,他引:2
Parisi G Perales M Fornasari MS Colaneri A González-Schain N Gómez-Casati D Zimmermann S Brennicke A Araya A Ferry JG Echave J Zabaleta E 《Plant molecular biology》2004,55(2):193-207
Three genes from Arabidopsis thaliana with high sequence similarity to gamma carbonic anhydrase (γCA), a Zn containing enzyme from Methanosarcina thermophila(CAM), were identified and characterized. Evolutionary and structural analyses predict that these genes code for active forms
of γCA. Phylogenetic analyses reveal that these Arabidopsis gene products cluster together with CAM and related sequences
from α and γ proteobacteria, organisms proposed as the mitochondrial endosymbiont ancestor. Indeed, in vitro and in vivo experiments indicate that these gene products are transported into the mitochondria as occurs with several mitochondrial
protein genes transferred, during evolution, from the endosymbiotic bacteria to the host genome. Moreover, putative CAM orthologous
genes are detected in other plants and green algae and were predicted to be imported to mitochondria. Structural modeling
and sequence analysis performed in more than a hundred homologous sequences show a high conservation of functionally important
active site residues. Thus, the three histidine residues involved in Zn coordination (His 81, 117 and 122), Arg 59, Asp 61,
Gin 75, and Asp 76 of CAM are conserved and properly arranged in the active site cavity of the models. Two other functionally
important residues (Glu 62 and Glu 84 of CAM) are lacking, but alternative amino acids that might serve to their roles are
postulated. Accordingly, we propose that photosynthetic eukaryotic organisms (green algae and plants) contain γCAs and that
these enzymes codified by nuclear genes are imported into mitochondria to accomplish their biological function. 相似文献
89.
The metabolism of 25-hydroxyvitamin D(3) was studied with a crude mitochondrial cytochrome P450 extract from pig kidney and with recombinant human CYP27A1 (mitochondrial vitamin D(3) 25-hydroxylase) and porcine CYP2D25 (microsomal vitamin D(3) 25-hydroxylase). The kidney mitochondrial cytochrome P450 catalyzed the formation of 1alpha,25-dihydroxyvitamin D(3), 24,25-dihydroxyvitamin D(3) and 25,27-dihydroxyvitamin D(3). An additional metabolite that was separated from the other hydroxylated products on HPLC was also formed. The formation of this 25-hydroxyvitamin D(3) metabolite was dependent on NADPH and the mitochondrial electron transferring protein components. A monoclonal antibody directed against purified pig liver CYP27A1 immunoprecipitated the 1alpha- and 27-hydroxylase activities towards 25-hydroxyvitamin D(3) as well as the formation of the unknown metabolite. These results together with substrate inhibition experiments indicate that CYP27A1 is responsible for the formation of the unknown 25-hydroxyvitamin D(3) metabolite in kidney. Recombinant human CYP27A1 was found to convert 25-hydroxyvitamin D(3) into 1alpha,25-dihydroxyvitamin D(3), 25,27-dihydroxyvitamin D(3) and a major metabolite with the same retention time on HPLC as that formed by kidney mitochondrial cytochrome P450. Gas chromatography-mass spectrometry (GC-MS) analysis of the unknown enzymatic product revealed it to be a triol different from other known hydroxylated 25-hydroxyvitamin D(3) metabolites such as 1alpha,25-, 23,25-, 24,25-, 25,26- or 25,27-dihydroxyvitamin D(3). The product had the mass spectrometic properties expected for 4beta,25-dihydroxyvitamin D(3). Recombinant porcine CYP2D25 converted 25-hydroxyvitamin D(3) into 1alpha,25-dihydroxyvitamin D(3) and 25,26-dihydroxyvitamin D(3). It can be concluded that both CYP27A1 and CYP2D25 are able to carry out multiple hydroxylations of 25-hydroxyvitamin D(3). 相似文献
90.