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排序方式: 共有371条查询结果,搜索用时 671 毫秒
141.
M G Melis C Troffa P Manunta P Pinna Parpaglia A Soro F Pala P Madeddu A Pazzola G Tonolo G Patteri 《Bollettino della Società italiana di biologia sperimentale》1990,66(7):679-684
Erythrocyte cation transport, plasma prorenin and renin and sexual hormones were sequentially evaluated in 12 normal volunteers over the menstrual cycle. Na-K cotransport and Na-Li countertransport raised in 6 out of 12 subjects in synchronization with the ovulatory phase. When the maximal % variation (ovulatory phase) versus baseline (follicular phase) of the Na-K cotransport was plotted versus the maximal % increment of oestrogens. A direct, highly significant inverse correlation was observed (r = 0.904, p less than 0.001). Moreover, a highly significant inverse correlation between plasma prorenin and intraerythrocyte Na (r = -0.857, p less than 0.001) in the follicular phase was found. Our data suggest that erythrocyte cation transport can be influenced by sexual hormones in human. 相似文献
142.
143.
Chloroplast Response in Dunaliella salina to Irradiance Stress (Effect on Thylakoid Membrane Protein Assembly and Function) 总被引:2,自引:1,他引:1
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The chloroplast response in the green alga Dunaliella salina to irradiance stress was investigated. Cells were grown under low light (LL) at 100 [mu]mol photons m-2 s-1 or high light (HL) at 2000 [mu]mol photons m-2 s-1 incident intensity. LL-grown cells had a low chlorophyll (Chl) a/b ratio, an abundance of light-harvesting complex II proteins (LHC-II), and a large Chl antenna size. HL-grown cells had a higher Chl a/b ratio, relatively fewer LHC-II, and a small Chl antenna size. The more abundant higher molecular mass subunits of the LHC-II (approximately 31 kD) were selectively depleted from the thylakoid membrane of HL-grown cells. Light-shift experiments defined the kinetics of change in the subunit composition of the LHC-II and suggested distinct mechanisms in the acclimation of thylakoids to HL or LL conditions. The results showed that irradiance exerts a differential regulation on the expression of various Lhcb genes. The specific polyclonal antibodies used in this work, raised against the purified LHC-II, cross-reacted with a polypeptide of approximately 20 kD in HL-grown samples. In this work we examined the dynamics of induction of this novel protein and discuss its function in terms of a chloroplast response to the level of irradiance. 相似文献
144.
The light-dependent rate of photosystem-II (PSII) damage and repair was measured in photoautotrophic cultures of Dunaliella salina Teod. grown at different irradiances in the range 50–3000 mol photons · m–2· s–1. Rates of cell growth increased in the range of 50–800 mol photons·m–2·s–1, remained constant at a maximum in the range of 800–1,500 mol photons·m–2 ·s–1, and declined due to photoinhibition in the range of 1500–3000 mol photons·m–2·s–1. Western blot analyses, upon addition of lincomycin to the cultures, revealed first-order kinetics for the loss of the PSII reaction-center protein (D1) from the 32-kDa position, occurring as a result of photodamage. The rate constant of this 32-kDa protein loss was a linear function of cell growth irradiance. In the presence of lincomycin, loss of the other PSII reaction-center protein (D2) from the 34-kDa position was also observed, occurring with kinetics similar to those of the 32-kDa form of D1. Increasing rates of photodamage as a function of irradiance were accompanied by an increase in the steady-state level of a higher-molecular-weight protein complex ( 160-kDa) that cross-reacted with D1 antibodies. The steady-state level of the 160-kDa complex in thylakoids was also a linear function of cell growth irradiance. These observations suggest that photodamage to D1 converts stoichiometric amounts of D1 and D2 (i.e., the D1/D2 heterodimer) into a 160-kDa complex. This complex may help to stabilize the reaction-center proteins until degradation and replacement of D1 can occur. The results indicated an intrinsic half-time of about 60 min for the repair of individual PSII units, supporting the idea that degradation of D1 after photodamage is the rate-limiting step in the PSII repair process.Abbreviations Chl
chlorophyll
- PSI
photosystem I
- PSII
photosystem II
- D1
the 32-kDa reaction-center protein of PSII, encoded by the chloroplast psbA gene
- D2
the 34-kDa reactioncenter protein of PSII, encoded by the chloroplast psbD gene
- QA
primary electron-accepting plastoquinone of PSII
The work was supported by grant 94-37100-7529 from the US Department of Agriculture, National Research Initiative Competitive Grants Program. 相似文献
145.
The organization of the electron transport components in mesophyll and bundle sheath chloroplasts of Zea mays was investigated. Grana-containing mesophyll chloroplasts (chlorophyll a to chlorophyll b ratio of about 3.0) possessed the full complement of the various electron transport components, comparable to chloroplasts from C3 plants. Agranal bundle sheath chloroplasts () contained the full complement of photosystem (PS) I and of cytochrome (cyt) f but lacked a major portion of PS II and its associated Chl light-harvesting complex (LHC), and most of the cyt b559. The kinetic analysis of system I photoactivity revealed that the functional photosynthetic unit size of PS I was unchanged and identical in mesophyll and bundle sheath chloroplasts. The results suggest that PS I is contained in stroma-exposed thylakoids and that it does not receive excitation energy from the Chl LHC present in the grana. A stoichiometric parity between PS I and cyt f in mesophyll and bundle sheath chloroplasts indicates that biosynthetic and functional properties of cyt f and P700 are closely coordinated. Thus, it is likely that both cyt f and P700 are located in the membrane of the intergrana thylakoids only. The kinetic analysis of PS II photoactivity revealed the absence of PS IIαfrom the bundle sheath chloroplasts and helped identify the small complement of system II in bundle sheath chloroplasts as PS IIβ. The distribution of the main electron transport components in grana and stroma thylakoids is presented in a model of the higher plant chloroplast membrane system. 相似文献
146.
Anastasios Melis 《Journal of cellular biochemistry》1984,24(3):271-285
The light environment during plant growth determines the structural and functional properties of higher plant chloroplasts, thus revealing a dynamically regulated developmental system. Pisum sativum plants growing under intermittent illumination showed chloroplasts with fully functional photosystem (PS) II and PSI reaction centers that lacked the peripheral chlorophyll (Chi) a/b and Chl a light-harvesting complexes (LHC), respectively. The results suggest a light flux differential threshold regulation in the biosynthesis of the photosystem core and peripheral antenna complexes. Sun-adapted species and plants growing under far-red-depleted illumination showed grana stacks composed of few (3–5) thylakoids connected with long intergrana (stroma) thylakoids. They had a PSII/PSI reaction center ratio in the range 1.3–1.9. Shade-adapted species and plants growing under far-red-enrichcd illumination showed large grana stacks composed of several thylakoids, often extending across the entire chloroplast body, and short intergrana stroma thylakoids. They had a higher PSII/PSI reaction center ratio, in the range of 2.2–4.0. Thus, the relative extent of grana and stroma thylakoid formation corresponds with the relative amounts of PSII and PSI in the chloroplast, respectively. The structural and functional adaptation of the photosynthetic membrane system in response to the quality of illumination involves mainly a control on the rate of PSII and PSI complex biosynthesis. 相似文献
147.
Direct measurements on the effective absorption cross-section of photosystem (PS) 1 were obtained with control (light — ATP) and phosphorylated (light + ATP) chloroplast thylakoids from spinach. The rate of light absorption by PS1 was invariant in control and phosphorylated thylakoids, suggesting a constant functional antenna size for this photosystem. We conclude that phosphorylated chlorophyll a-b light-harvesting complex from PS2 is not functionally connected with the antenna pigment of PS1. 相似文献
148.
The amino acid sequence of the dihaem cytochrome c4 from the bacterium Azotobacter vinelandii. 总被引:2,自引:2,他引:0
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An amino acid sequence is proposed for the cytochrome c4 from the bacterium Azotobacter vinelandii strain OP. It is a single polypeptide chain of 190 residues, with two sets of haem-attachment cysteine residues at positions 14/17 and 119/122. Proteins with similar sequences are also present in denitrifying pseudomonads. There is similarity in sequence between the two halves of the cytochrome c4 molecule, and each half also shows similarity to the sequences of certain monohaem cytochromes c isolated from organisms that are not obviously closely related to A. vinelandii. Detailed evidence for the amino acid sequence of the protein has been deposited as Supplementary Publication SUP 50125 (17 pages) at the British Library Lending Division, Boston Spa, West Yorkshire LS23 7BQ, U.K., from whom copies are available on prepayment. 相似文献
149.
The effect of divalent cations on the primary photoconversion kinetics of chloroplast Photosystems (PS) I and II was investigated by absorbance difference spectrophotometry in the ultraviolet (ΔA320) and red (ΔA700) regions and by fluorescence at room temperature. Three main chlorophyll (Chl) a fluorescence emission components were identified. Addition of 5 mM MgCl2 to unstacked chloroplasts caused a 5–7-fold increase in Fvα, the variable fluorescence yield controlled by the α-centers. The fluorescence yield Fvβ controlled by the β-centers and the nonvariable fluorescence yield F0 were only slightly changed by the treatment. The absolute number of α- and β-centers remained unchanged and independent of divalent cations. The rate constants Kα, Kβ and KP-700 determined from the photoconversion kinetics of Qα, Qβ and P-700 were also unchanged by divalent cations, suggesting a constancy of the respective absorption cross-sections. Evidence is presented that the Mg2+ effect on Chl a fluorescence is not due simply to unstacking. Conclusion: (1) In the absence of divalent cations from the chloroplast suspending medium, the variable fluorescence yield is not complementary to the rate of PS II photochemistry. (2) A spillover of excitation from PS II to PS I in the absence of Mg2+ cannot account for the 7-fold lowering of the variable fluorescence yield Fvα at room temperature. The results are discussed in view of a model of excitation transfer and fluorescence emission in the pigment bed of PS IIα and PS IIβ. 相似文献
150.
Parental origin and germline mosaicism of deletions and duplications of the dystrophin gene: a European study 总被引:12,自引:0,他引:12
Anthonie J. van Essen Stephen Abbs Montserrat Baiget Egbert Bakker Catherine Boileau Christine van Broeckhoven Kate Bushby Angus Clarke Mireille Claustres Angela E. Covone Maurizio Ferrari Alessandra Ferlini Giuliana Galluzzi Tiemo Grimm Caroline Grubben Marc Jeanpierre Helena Kääriäinen Sabina Liechti-Gallati Marie A. Melis Gert-J. B. van Ommen Jaques E. Poncin Hans Scheffer Marianne Schwartz Astrid Speer Manfred Stuhrmann Christine Verellen-Dumoulin Douglas E. Wilcox Leo P. ten Kate 《Human genetics》1992,88(3):249-257
Summary Knowledge about the parental origin of new mutations and the occurrence of germline mosaicism is important for estimating recurrence risks in Duchenne (DMD) and Becker muscular dystrophy (BMD). However, there are problems in resolving these issues partly because not all mutations can as yet be directly detected, and additionally because genetic ratios are very sensitive to ascertainment bias. In the present study, therefore, analysis was restricted to currently detectable mutations (deletions and duplications) in particular types of families which tend to be rare. In order to obtain sufficient data we pooled results from 25 European centers. In mothers of affected patients who were the first in their family with a dystrophin gene deletion or duplication, the ratio between the paternal and the maternal origin of this new mutation was 32:49 (binomial test P = 0.075) for DMD. In five BMD families the ratio between paternal and maternal origin of new mutations was 32. Recurrence risk because of maternal germline mosaicism was studied in sisters or subsequent sibs of isolated cases with an apparently new detectable mutation. In 12 out of 59 (0.20; 95% CI 0.10–0.31) transmissions of the risk haplotype the DMD mutation was transmitted as well. No recurrences were found in nine BMD families. 相似文献