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41.
Alexander N. Glazer Yvonne M. Gindt Crystal F. Chan Kenneth Sauer 《Photosynthesis research》1994,40(2):167-173
Efficient production of ATP and NADPH by the light reactions of oxygen-evolving photosynthesis demands continuous adjustment of transfer of absorbed light energy from antenna complexes to Photosystem I (PS I) and II (PS II) reaction center complexes in response to changes in light quality. Treatment of intact cyanobacterial cells with N-ethylmaleimide appears to disrupt energy transfer from phycobilisomes to Photosystem I (PS I). Energy transfer from phycobilisomes to Photosystem II (PS II) is unperturbed. Spectroscopic analysis indicates that the individual complexes (phycobilisomes, PS II, PS I) remain functionally intact under these conditions. The results are consistent with the presence of connections between phycobiliproteins and both PS II and PS I, but they do not support the existence of direct contacts between the two photosystems.Abbreviations Chl
chlorophyll
- EPR
electron paramagnetic resonance
- NEM
N-ethylmaleimide
- PBS
phycobilisome
- PS
photosystem 相似文献
42.
Manfred Gahrtz Jürgen Stolz Norbert Sauer 《The Plant journal : for cell and molecular biology》1994,6(5):697-706
In this paper the cloning of a full-length cDNA clone encoding the PmSUC2 sucrose-H+ symporter from Plantago major is described. This plant allows the simple preparation of vascular bundles from the basal regions of fully developed source leaves and thus a separation of vascular and non-vascular tissue. A cDNA library was constructed from poly(A)+ RNA isolated from vascular bundles and used for the subsequent cloning of cDNAs. The respective mRNA is specifically expressed in the vascular bundles as shown on Northern blots of total RNA from vascular and non-vascular tissues. The PmSUC2 protein has 12 putative transmembrane helices and is highly homologous to other plant sucrose transporters. Substrate specificity and energy dependence of the transporter encoded by this cDNA were determined by expression in baker's yeast Saccharomyces cerevisiae. The PmSUC2 protein catalyses the transport of sucrose into transgenic yeast cells. Invertase null mutants of yeast expressing PmSUC2 accumulate sucrose more than 200-fold. This transport was sensitive to uncouplers or SH-group inhibitors. Plasma membranes from yeast cells expressing the PmSUC2 protein were purified and fused to proteoliposomes containing cytochrome-c-oxidase. In this system sucrose is accumulated only when proton motive force is generated, indicating that PmSUC2 is a sucrose-H+ symporter. The apparent molecular weight of the PmSUC2 protein is 35 kDa on 10% SDS-polyacrylamide gels. The presented data strongly support the theory of phloem loading from the apoplastic space by a sucrose-H+ symporter. 相似文献
43.
The nature of replication origins in eukaryotic chromosomes has been examined in some detail only in yeast, Drosophila, and mammalian cells. We have used highly synchronous cultures of plasmodia of the myxomycete Physarum and two-dimensional agarose gel electrophoresis to examine replication of two developmentally controlled, early replicated genes over time in S-phase. A single, discrete origin of replication was found within 4.8 kb of the LAV1-5 gene, which encodes a homolog of profilin. In contrast, the LAV1-2 gene appears to be surrounded by several origins. Two origins were identified within a 15 kb chromosomal domain and appear to be inefficiently used. Replication forks collide at preferred sites within this domain. These terminating structures are long lived, persisting for at least 2 h of the 3 h S-phase. Analysis of restriction fragment length polymorphisms (RFLPs) within the LAV1-2 domain indicates that replication of alleles on different parental chromosomes is a highly coordinated process. Our studies of the these two early replicated, plasmodium-specific genes indicate that both a fixed, narrow origin region and a broader zone containing two closely spaced origins of DNA replication occur in Physarum. 相似文献
44.
45.
Suzanne Demczuk Annie Lévy Muriel Aubry Marie-Françoise Croquette Nicole Philip Marguerite Prieur Ursula Sauer Patrice Bouvagnet Guy A. Rouleau Gilles Thomas Alain Aurias 《Human genetics》1995,96(1):9-13
We have determined the parental origin of the deleted chromosome 22 in 29 cases of DiGeorge syndrome (DGS) using a CA-repeat mapping within the commonly deleted region, and in one other case by using a chromosome 22 short arm heteromorphism. The CA-repeat was informative in 21 out of 29 families studied and the deleted chromosome was of maternal origin in 16 cases (72%). When these data are pooled with recent results from the literature, 24 de novo DGS, velo-cardio-facial syndrome (VCFS) and isolated conotruncal cardiac disease deletions are found to be of maternal origin and 8 of paternal origin, yielding a 2 of 8 with a probability level lower than 0.01. These data, and review of the literature on familial DGS/VCFS and isolated conotruncal cardiopathies suggest that there is a strong tendency for the 22q11.2 deletions to be of maternal origin. 相似文献
46.
The ability of salts to inhibit the O2-evolution activity of PS II preparations is shown to parallel closely the Hofmeister series, suggesting that inhibition is related to the solubility of the 16, 24 and 33 kDa proteins in these salt solutions. An examination of the effect of salt inactivation on the low temperature multiline EPR signal indicates that the release of either the 16 and 24 kDa proteins, or additionally the 33 kDa protein blocks or greatly reduces the efficiency of the advancement of the water-splitting complex to the S2-state; under some conditions, this inhibition is reversible. 相似文献
47.
The amino-terminal sequences have been determined by Edman degradation for the reaction center polypeptides from a carotenoidless mutant of Rhodopseudomonas capsulata. Individual polypeptides were isolated by preparative electrophoresis and electroelution. By comparison with the sequences deduced from the DNA (Youvan, D.C., Alberti, M., Begush, H., Bylina, E.J. and Hearst, J.E. (1984) Proc. Natl. Acad. Sci. USA 81, 189–192) we conclude that the M and L subunits are processed so as to remove the amino-terminal methionine, whereas the H subunit is not processed at the amino-terminus after translation. None of the subunits is synthesized with a significant amino-terminal extension peptide. 相似文献
48.
In Photosystem II preparations at low temperature we were able to generate and trap an intermediate state between the S1 and S2 states of the Kok scheme for photosynthetic oxygen evolution. Illumination of dark-adapted, oxygen-evolving Photosystem II preparations at 140 K produces a 320-G-wide EPR signal centered near g = 4.1 when observed at 10 K. This signal is superimposed on a 5-fold larger and somewhat narrower background signal; hence, it is best observed in difference spectra. Warming of illuminated samples to 190 K in the dark results in the disappearance of the light-induced g = 4.1 feature and the appearance of the multiline EPR signal associated with the S2 state. Low-temperature illumination of samples prepared in the S2 state does not produce the g = 4.1 signal. Inhibition of oxygen evolution by incubation of PS II preparations in 0.8 M NaCl buffer or by the addition of 400 μM NH2OH prevents the formation of the g = 4.1 signal. Samples in which oxygen evolution is inhibited by replacement of Cl? with F? exhibit the g = 4.1 signal when illuminated at 140 K, but subsequent warming to 190 K neither depletes the amplitude of this signal nor produces the multiline signal. The broad signal at g = 4.1 is typical for a spin system in a rhombic environment, suggesting the involvement of non-heme Fe in photosynthetic oxygen evolution. 相似文献
49.
Negative correlation between protozoal and bacterial levels in rumen samples and its relation to the determination of dietary effects on the rumen microbial population. 总被引:2,自引:1,他引:1 下载免费PDF全文
The bacterial protein content and protozoal protein content of unfractionated samples from the liquid-small particle phase of the rumen were determined on the basis of direct microscopic measurement of bacteria numbers and protozoa numbers and cell volumes. Standard values of 8.7 X 10(-11) mg of protein per bacterial cell and 5.9 X 10(-11) mg/micron 3 of protozoa cell volume, obtained from analysis of isolated cells, were used to convert the microscopic measurements to an estimate of the protein content of the rumen sample. When the correlation between bacterial and protozoal protein levels was examined within groups of animals, a highly significant negative correlation between these two parameters was found (P less than 0.001). The variation among animals for total (bacterial plus protozoal) microbial protein was smaller than the variation among animals for bacterial or protozoal protein alone. There was also a highly significant positive correlation (P less than 0.001) between protozoal protein level and total microbial protein level. The variation found among animals in total microbial protein level could be reduced by using a regression equation determined for bacterial versus protozoal protein to correct for the different population dynamics of the two groups. 相似文献
50.
Methane synthesis by membrane vesicles and a cytoplasmic cofactor isolated from Methanobacterium thermoautotrophicum. 总被引:6,自引:1,他引:5 下载免费PDF全文
Methanobacterium thermoautotrophicum when grown on ordinary culture medium has a tough cell wall which is lysozyme-resistant and difficult to disrupt by physical means. The cell wall, however, can be weakened by the addition of D-sorbitol to the growth medium and the organisms form protoplasts after lysozyme addition. This technique allowed the isolation of two types of intracellular small vesicles: (a) isolated by disruption of the total cell population (lysozyme-sensitive and lysozyme-resistant cells) by ultrafrequency sound and (b) isolated by osmotic lysis of protoplasts. For the first time, a small vesicle fraction isolated as in (a) was capable of synthesizing methane from CO2 and H2 without cytoplasm. There was, however, an absolute requirement for a small, heat-stable, oxygen-sensitive cofactor which was isolated from the cytoplasm. Methane synthesis with this vesicle fraction was inhibited by the detergent deoxycholate, and by the protonophores 2,4-dinitrophenol and carbonyl cyanide m-chlorophenylhydrazone. Mg2+-ATPase appeared to be located on the outer or cytoplasmic surface of the small vesicle fraction isolated as in (b). The results were consistent with a previously made suggestion [Sauer, Erfle & Mahadevan (1981) J. Biol. Chem. 256, 9843-9848] that the interior of the small intracellular vesicles becomes acid during methane synthesis. 相似文献