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101.
Bundle sheath strands free of mesophyll contamination were isolated from 3–4-week-old leaves of maize (Zea mays L.). Patterns of electron flow in the preparations were studied in the presence of physiological substrates. Relative electron flow rates were estimated from the flash-induced electrochromic band shift changes (P-518) and cytochrome f turnover. Induction of chlorophyll fluorescence was also measured. Little Photosystem II activity was found to be present, the principal pathway of electron flow being Photosystem I-driven cyclic electron transfer. The latter was activated through reductive poising by NADPH, generated via malate decarboxylation or (less efficiently) from dihydroxyacetone phosphate. The actions of these electron donors and of oxygen, nitrite and methyl viologen as electron acceptors in redox poising the Photosystem I-driven cycle were investigated and are discussed in relation to the regulation of photosynthesis in the bundle sheath. 相似文献
102.
The pathways through which NADPH, NADH and H2 provide electrons to nitrogenase were examined in anaerobically isolated heterocysts. Electron donation in freeze-thawed heterocysts and in heterocyst fractions was studied by measuring O2 uptake, acetylene reduction and reduction of horse heart cytochrome c. In freeze-thawed heterocysts and membrane fractions, NADH and H2 supported cyanide-sensitive, respiratory O2 uptake and light-enhanced, cyanide-insensitive uptake of O2 resulting from electron donation to O2 at the reducing side of Photosystem I. Membrane fractions also catalyzed NADH-dependent reduction of cytochrome c. In freeze-thawed heterocysts and soluble fractions from heterocysts, NADPH donated electrons in dark reactions to O2 or cytochrome c through a pathway involving ferredoxin:NADP reductase; these reactions were only slightly influenced by cyanide or illumination. In freeze-thawed heterocysts provided with an ATP-generating system, NADH or H2 supported slow acetylene reduction in the dark through uncoupler-sensitive reverse electron flow. Upon illumination, enhanced rates of acetylene reduction requiring the participation of Photosystem I were observed with NADH and H2 as electron donors. Rapid NADPH-dependent acetylene reduction occurred in the dark and this activity was not influenced by illumination or uncoupler. A scheme summarizing electron-transfer pathways between soluble and membrane components is presented. 相似文献
103.
Intact vacuoles were isolated from petals of Hippeastrum and Tulipa (Wagner G.J. and Siegelman, H.W. (1975) Science 190, 1298--1299). The ATPase activity of fresh vacuole suspensions was found to be 2--3 times that of protoplasts from the same tissue. 70--80% of the ATPase activity of intact vacuoles was recovered in tonoplast preparations. The antibiotic Dio-9 at 6mug/10(6) vacuoles or protoplasts causes 40% inhibition. However, only the protoplast ATPase is sensitive to oligomycin. N,N'-dicyclohexylcarbodiimide (DCCD) slightly stimulates ATPase activity in both vacuole and protoplast suspensions, whereas ethyl-3-(3-dimethylaminopropyl carbodiimide) (EDAC) strongly inhibits. Spectrophotometric studies show that in the petal the vacuolar contents have a pH of 4.0 for Tuplipa and 4.3 for Hippeastrum, whereas the intact isolated vacuole has an internal pH of 7.0 (in pH 8.0 buffer) for (Tulipa and about 7.3 for Hippeastrum. Internal ion concentrations of 150, 46, 30, 30 and 6 mM were found for K+, Na+, Mg2+, Cl-, and Ca2+ respectively, which are about the same as those in protoplasts. 相似文献
104.
Intense illumination isolated, intact, spinach chloroplasts triggers the well known proton-pumping Mg2+ ATPase activity of coupling factor, which can be assayed in subsequently lysed chloroplasts by monitoring ATP-driven quenching of 9-aminoacridine fluorescence. The light-triggered ATPase activity decays slowing in the dark and is inhibited by N,N'-dicyclohexylcarbodiimide. After osmotic lysis and washing of the chloroplasts, preillumination no longer triggers maximal proton-pumping ATPase until methylviologen and dithiothreitol are added to the medium. It is suggested that intact organelles contain soluble or loosely bound cofactors necessary for light-triggering of coupling factor ATPase. On osmotic lysis, these endogenous cofactors are diluted or inactivated and must be replaced by addition of a dithiol reagent and an electron acceptor. 相似文献
105.
Intense illumination of isolated, intact, spinach chloroplasts triggers the well known proton-pumping Mg2+ ATPase activity of coupling factor, which can be assayed in subsequently lysed chloroplasts by monitoring ATP-driven quenching of 9-aminoacridine fluorescence. The light-triggered ATPase activity decays slowly in the dark and is inhibited by N,N′-dicyclohexylcarbodiimide. After osmotic lysis and washing of the chloroplasts, preillumination no longer triggers maximal proton-pumping ATPase until methylviologen and dithiothreitol are added to the medium. It is suggested that intact organelles contain soluble or loosely bound cofactors necessary for light-triggering of coupling factor ATPase. On osmotic lysis, these endogenous cofactors are diluted or inactivated and must be replaced by addition of a dithiol reagent and an electron acceptor. 相似文献
106.
Haÿ E Lemonnier J Fromigué O Guénou H Marie PJ 《The Journal of biological chemistry》2004,279(3):1650-1658
Bone morphogenetic protein-2 (BMP-2) is an important regulator of osteoblast differentiation. However, the regulation of osteoblast apoptosis by BMP signaling remains poorly understood. Here we examined the role of type I BMP receptor (BMP-RI) in osteoblast apoptosis promoted by BMP-2. Despite undetectable BMP-RIB expression in OHS4 cells, BMP-2 or BMP-2 overexpression increased osteoblast differentiation similarly as in SaOS2 cells which express BMP-RIB, as shown by alkaline phosphatase and CBFA1/RUNX2 expression. In contrast to SaOS2 cells, however, BMP-2 or BMP-2 overexpression did not increase caspase-9 and caspases-3, -6, and -7 activity and DNA fragmentation in OHS4 cells. Consistently, BMP-2 increased protein kinase C (PKC) activity, and PKC inhibition suppressed BMP-2-induced caspase activity in SaOS2 but not in OHS4 cells that lack BMP-RIB. A dominant negative BMP-RIB inhibited BMP-2-induced caspase activity, whereas wild-type BMP-RIB promoted caspase activity induced by BMP-2 in SaOS2 and MC3T3-E1 cells. Wild-type BMP-RIB rescued the apoptotic response to BMP-2, and a constitutively active BMP-RIB restored the apoptotic signal in OHS4 cells, supporting an essential role for BMP-RIB in osteoblast apoptosis. We also assessed whether BMP-2-induced apoptosis occurred independently of osteoblast differentiation. General inhibition of caspases did not abolish BMP-2-induced alkaline phosphatase and CBFA1/RUNX2 expression in SaOS2 cells. Furthermore, broad caspases inhibition increased matrix mineralization but did not reverse the BMP-2 effect on mineralization in MC3T3-E1 cells. These results indicate that BMP-2-induced apoptosis was mediated by BMP-RIB in osteoblasts and occurred independently of BMP-2-induced osteoblast differentiation, which provides additional insights into the dual mechanism of BMP-2 action on osteoblast fate. 相似文献
107.
108.
Hind G 《Plant physiology》1966,41(7):1237-1239
The uncoupler desaspidin is labile in the presence of oxidants at alkaline pH values. It also undergoes chlorophyll-sensitized photooxidation at a more acid pH. The products of the oxidation appear to have negligible activity in inhibiting electron transfer and photophosphorylation. 相似文献
109.
Folding recombinant spider‐silk in H2O: Effect of osmolytes on the solution conformation of a 15‐repeat spider‐silk mimetic
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Glendon D. McLachlan Babak Gandjian Hind Alhumaidan 《Protein science : a publication of the Protein Society》2016,25(10):1853-1862
The folding of a recombinant spider silk protein‐polymer in the presence of the tri‐methylamine osmolytes TMANO and Betaine in 80% H2O is reported. Circular dichroism measurements (CD) reveal an increase in α‐helical secondary structure with increasing osmolyte concentrations, as determined by an increase in ellipticity at 222 nm. Consistent with this observation, the signal for random coil sampling, observed at 205 nm, is greatly reduced with increasing trimethylamine. Fluorescence spectra of a single tyrosine positioned within the conserved 33‐amino acid repeat primary sequence (of the spider‐silk mimetic) complements the conformational changes observed by CD. Importantly, there is a correlation between the number of Alkyl‐groups (CH3‐) on the amine of the osmolyte and enhanced helicity of the 15‐repeat silk‐mimetic for the osmolytes tested, ie TMANO, Betaine, Sarcosine and Glycine. These preliminary results are applicable to storing and processing recombinant silk sequences in H2O, an important mile‐stone for widespread use of recombinant silk polymers. 相似文献
110.
Jacqueline London Claude Rouch Linh Chi Bui Elodie Assayag Benoit Souchet Fabrice Daubigney Hind Medjaoui Serge Luquet Christophe Magnan Jean Maurice Delabar Julien Dairou Nathalie Janel 《Molecular neurobiology》2018,55(5):3822-3831
Trisomy 21 (T21) or Down syndrome (DS) is the most common genetic disorder associated with intellectual disability and affects around 5 million persons worldwide. Neuroanatomical phenotypes associated with T21 include slight reduction of brain size and weight, abnormalities in several brain areas including spines dysgenesis, dendritic morphogenesis, and early neuroanatomical characteristics of Alzheimer’s disease. Monoamine neurotransmitters are involved in dendrites development, functioning of synapses, memory consolidation, and their levels measured in the cerebrospinal fluid, blood, or brain areas that are modified in individuals with T21. DYRK1A is one of the recognized key genes that could explain some of the deficits present in individuals with T21. We investigated by high-performance liquid chromatography with electrochemical detection the contents and processing of monoamines neurotransmitters in four brain areas of female and male transgenic mice for the Dyrk1a gene (mBactgDyrk1a). DYRK1A overexpression induced dramatic deficits in the serotonin contents of the four brain areas tested and major deficits in dopamine and adrenaline contents especially in the hypothalamus. These results suggest that DYRK1A overexpression might be associated with the modification of monoamines content found in individuals with T21 and reinforce the interest to target the level of DYRK1A expression as a therapeutic approach for persons with T21. 相似文献