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121.
Using differently labelled precursors, it was established that rhododendrin (3-(4-hydroxyphenyl)-1-methylpropyl-β-D-glucopyranoside) is formed through the phenylpropane pathway via p-coumaryl alcohol, dihydro-p-coumaryl alcohol and C-methylation of the γ-C-atom of the C6C3 unit with methionine supplying the methyl group. It was demonstrated that the pro-(S)-hydrogen atom of dihydro-p-coumaryl alcohol is replaced stereospecifically by the methyl group. 相似文献
122.
Light and dark assimilation of nitrate in plants 总被引:6,自引:3,他引:3
Abstract. Heterotrophic assimilation of nitrate in roots and leaves in darkness is closely linked with the oxidative pentose phosphate pathway. The supply of glucose-6-phosphate to roots and chloroplasts in leaves in darkness is essential for assimilation of nitrite into amino acids. When green leaves are exposed to light, the key enzyme, glucoses-phosphate dehydrogenase, is inhibited by reduction with thioredoxin. Hence the dark nitrate assimilatory pathway is inhibited under photoautotrophic conditions and replaced by regulatory reactions functioning in light. On account of direct photo-synthetic reduction of nitrite in chloroplasts and availability of excess NADH for nitrate reduclase, the rate of nitrate assimilation is extremely rapid in light. Under dark anaerobic conditions also nitrate is equally rapidly reduced to nitrite on account of abolition of competition for NADH between nitrate reductase and mitochondrial oxidation. 相似文献
123.
实验结果表明:照光时绿豆叶片分离线粒体通过细胞色素氧化酶途径的NADH氧化部分受阻,电子转向交替途径。不产生能量,不受能荷控制的NADH氧化途径有利于绿色细胞线粒体在光合作用时执行其提供碳架的功能。看来绿色细胞线粒体本身具有对光的敏感性,在照光时调节呼吸途径以适应其功能的转换。呼吸途径的转换机制目前还不清楚。绿豆种子线粒体与叶片线粒体不同,没有上述的这种对光的反应。 相似文献
124.
Enzyme activities were determined quantitatively in individual rat oocytes to study their energy metabolism during maturation. Low hexokinase activity and high activities of lactate dehydrogenase and enzymes in the phosphate pathway, i.e., glucose 6-P and 6-P gluconate dehydrogenases, were characteristic of immature oocytes. Hexokinase may be a rate-limiting enzyme that enables oocytes to use glucose as an energy source. During maturation, the activities of hexokinase, phosphofructokinase, and malate dehydrogenase increased significantly, suggesting that the glycolytic pathway, as well as the tricarboxylic acid cycle, developed as the first meiotic division proceeded. In contrast, the activities of glucose 6-P and 6-P gluconate dehydrogenases decreased in maturing oocytes. The observation that the enzyme pattern in mature oocytes resembles more closely that in somatic cells appears to be significant, especially in light of previous studies showing this developmental trend in preimplantation embryos. 相似文献
125.
Pea chloroplastic phosphoribulokinase and yeast phosphoriboisomerase partition independently of one another in a two-phase polyethyleneglycol, dextran system, but apparent interaction is seen when ribose-5-phosphate is added to the two-phase system. It appears that the pea leaf of kinase recognizes yeast isomerase when it is carrying metabolite. 相似文献
126.
Non-green plastids (leucoplasts) isolated from pea roots are shown to be considerably active in forming aromatic amino acids by the shikimate pathway which, in contrast to the chloroplast pathway, is independent of light. Supply of phosphoenolpyruvate and 3-dehydroquinate, 3-dehydroshikimate, shikimate and quinate effectively enhances the formation of aromatic amino acids suggesting an intra- or/and intercellular intermediate transport. 相似文献
127.
Interaction between induction of carbonic anhydrase (CA) activity, induction of inorganic carbon (Ci ) concentrating mechanisms and the photorespiratory glycolate pathway has been studied in wild type 6145c and photorespiratory mutant 18–7F (low in phosphoglycolate phosphatase activity) cells of C. reinhardtii . Cell transfer from high CO2 (5%, v/v) to low CO2 (0.03%) provoked an increase of extracellular and total (extracellular plus intracellular) CA in both wild type and mutant cells. During adaptation to low CO2 conditions, both strains excreted ammonium to the medium at a similar rate in the presence of l -methionine- d-l -sulfoximine (MSX), an inhibitor of glutamine synthetase (GS). MSX also provoked ammonium excretion by air adapted wild type and mutant cells, even though both strains had high levels of CA activity and of Ci concentrating activities.
GS increased in both strains after transfer from high to low CO2 conditions. However, this increase was abolished by aminooxyacetate, an inhibitor of the glyoxylate-serine aminotransferase, and by glycolaldehyde, an inhibitor of triose phosphate to ribulose 1,5-bisphosphate conversion. CA synthesis did not occur in the presence of either aminooxyacetate or glycolaldehyde. Algae grown in high CO2 in the presence of aminooxyacetate did not induce Ci concentrating mechanisms. Integration of these three processes, i.e., CA synthesis, Ci -concentration, and photorespiratory glycolate pathway is proposed in the framework of carbon metabolism of the alga. 相似文献
GS increased in both strains after transfer from high to low CO
128.
David Mauzerall 《Photosynthesis research》1992,33(2):163-170
Living matter is an organized system which requires a continual flux of energy for its survival. As a working assumption, the flux of energy required for the origin of a self-duplicating cell is taken as the power required for the maintenance of a modern cell: 10 mW per g of carbon or some 105 times the output per gram of the sun. Solar photochemistry supplies the energy for the continuing evolution of life and, by continuity, for its origin. The iron oxide-sulfide photosynthetic unit proposed by S. Granick 35 years ago was meant to supply this energy. The evolution of complex organic photosensitizers is rationalized by the Granick hypothesis that biosynthetic pathways recapitulate their evolution. These concepts are discussed in the context of the evolution of photosynthetic systems and the known properties of these pigments. 相似文献
129.
SERGIO MOLINARI 《The Annals of applied biology》1991,119(2):373-379
The effect of nematode infestation on the alternative pathway respiration of mitochondria isolated from resistant and susceptible tomato roots greatly depended on the oxidisable substrate tested. The percentage of alternative respiration in NADH, malate and succinate oxidation was markedly different between the resistant (Rossol) and the susceptible (Roma VF) cultivars before infestation. Only the percentage of malate alternative oxidation in mitochondria from the resistant roots was influenced by nematode invasion. Conversely, attacked roots showed consistent variations in the content of mitochondria per unit fresh weight and in the phosphorylation efficiency (ADP/O) of the organelles. Expression of the alternative pathway (ρ' value) was found to be unchanged in intact roots and isolated mitochondria six days after nematode inoculation. 相似文献
130.
Dr. Peter Somogyi J. V. Priestley A. C. Cuello A. D. Smith J. P. Bolam 《Cell and tissue research》1982,223(3):469-486
Summary A monoclonal antibody that recognises the C-terminal part of substance P was used to study immunoreactive structures in the substantia nigra by the unlabeled antibody, peroxidase-antiperoxidase procedure. Immunoreactivity was present in nerve fibres in all parts of the substantia nigra, particularly in the pars reticulata and pars lateralis. Electron microscopically two types of bouton immunoreactive for substance P were found: Type 1 contained large electron-lucent vesicles, occasional large granulated vesicles and formed symmetrical synapses with dendrites. Type 2 boutons contained smaller, round electron-lucent vesicles, many large granular vesicles and formed asymmetrical synapses (having prominent postjunctional dense bodies) with dendrites and perikarya.Immunoreactive fibres with varicosities that had been identified light microscopically were studied in serial sections in the electron microscope. Each identified varicosity contained synaptic vesicles and formed a single synapse. An individual fibre formed boutons of only one kind (type 1 or type 2) and could form multiple synapses with the same neuron. Thus, an identified fibre in the pars compacta had eight varicosities, each of which was in synaptic contacts (type 2) with the dendrites or soma of the same neuron.The results are consistent with the concept that substance P is a synaptic transmitter in the substantia nigra and indicate that neurons in this region may receive a significant input from substance P-containing afferents, and that there are at least two types of such afferent fibres. 相似文献