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51.
Influence of respiration on photosynthesis in Synechocystis PCC6803 was studied by measuring the redox transients of cytochrome f (cyt f) upon excitation of the cells with repetitive single turnover flashes. Upon the addition of KCN the flash-induced oxidation of cyt f was increased and the rereduction of cyt f+ was accelerated. Dependence of these effects on the concentration of KCN clearly demonstrated the existence of two cyanide-sensitive oxidases interacting with photosynthesis: cyt aa3, which was sensitive to low concentrations of cyanide, and an alternative oxidase, which could be suppressed by using 1 mM KCN. The interaction between the photosynthetic and the respiratory electron transport chains was regulated mainly by the activity of the alternative cyanide-sensitive oxidase. The oxidative pathway involving the alternative cyanide-sensitive oxidase was insensitive to salicyl hydroxamic acid and azide. The close resemblance of the inhibition pattern reported here and that described for chlororespiration in algae and higher plants strongly suggest that an oxidase of the same type as the alternative cyanide-sensitive oxidase of cyanobacteria functions as a terminal oxidase in chloroplasts. 相似文献
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Zsófia Horváth Christophe Lejeusne Francisco Amat Javier Sánchez-Fontenla Csaba F. Vad Andy J. Green 《Hydrobiologia》2018,824(1):229-242
Long-term (1987–2015) monitoring data from Lake Lugano (Switzerland/Italy) were used to examine the effects of winter weather, solar radiation and mixing regime on the recovery of the trophic state of a lake undergoing nutrient management. Main hypotheses were that (H1) trends in trophic state were influenced not only by nutrient management, but also by winter weather and solar radiation, and (H2) the effects of management were more pronounced in the holomictic South basin than in the meromictic North basin of the lake. External loadings of phosphorus were strongly reduced during the study period, but key indicators of trophic state, including phosphorous concentration, primary production, chlorophyll a and deep-water oxygenation, showed inconsistent responses. Supporting H1, winter weather (parameterized using an index of the East Atlantic pattern) influenced temporal variation in phosphorus concentration and primary production in the North basin. Supporting H2, the effects of management on trophic state were clearer in the South basin, where most trophic-state indicators declined. Meromixis affected the restoration of the North basin lake by transmitting effects of climatic variation on trophic state. The added variability obscured the effects of restoration and caused sudden deteriorations in water quality, indicating that the restoration of meromictic lakes presents unique challenges. 相似文献
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This article suggests how we might understand the way potential predators see coloration patterns used in aposematism and
visual mimicry. We start by briefly reviewing work on evolutionary function of eyes and neural mechanisms of vision. Often
mechanisms used for achromatic vision are accurately modeled as adaptations for detection and recognition of the generality
of optical stimuli, rather than specific stimuli such as biological signals. Colour vision is less well understood, but for
photoreceptor spectral sensitivities of birds and hymenopterans there is no evidence for adaptations to species-specific stimuli,
such as those of food or mates. Turning to experimental work, we investigate how achromatic and chromatic stimuli are used
for object recognition by foraging domestic chicks (Gallus gallus). Chicks use chromatic and achromatic signals in different ways: discrimination of large targets uses (chromatic) colour
differences, and chicks remember chromatic signals accurately. However, detection of small targets, and discrimination of
visual textures requires achromatic contrast. The different roles of chromatic and achromatic information probably reflect
their utility for object recognition in nature. Achromatic (intensity) variation exceeds chromatic variation, and hence is
more informative about change in reflectance – for example, object borders, while chromatic signals yield more information about surface reflectance (object
colour) under variable illumination.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
57.
The free energy difference between folded and unfolded state is about the same for most proteins and it is not more than the energy of a few noncovalent interactions. In addition to the numerous noncovalent interactions, some proteins contain one or more disulfide bonds, which, as covalent crosslinks, significantly stabilize their tertiary structure. Correlation between the presence of disulfide bond(s), and the number noncovalent interresidue interactions of various kinds is analyzed here. The number of interactions per residue is almost the same for all protein. Also the number of long-range interactions per residue is the same in all proteins. Proteins with S(SINGLE BOND)S bond(s) (extracellular proteins) have more medium-range and fewer short-range interactions than those without S(SINGLE BOND)S bonds. However, the difference is independent of the number of these covalent crosslinks. We concluded that the different distributions of the various kinds of noncovalent interaction reflect the needs of proteins in the different environments, the extracellular and the intracellular ones, rather than the presence of the disulfide bond(s). We also pointed out that the observed differences in the distributions of short- and medium-range interactions are in good agreement with different secondary structure compositions of extracellular and intracellular proteins. Proteins 27:360–366, 1997. © 1997 Wiley-Liss, Inc. 相似文献
58.
Katharina Hiebler Zsófia Lengyel Carlos A. Castañeda Olga V. Makhlynets 《Proteins》2017,85(9):1656-1665
AlleyCatE is a de novo designed esterase that can be allosterically regulated by calcium ions. This artificial enzyme has been shown to hydrolyze p‐nitrophenyl acetate (pNPA) and 4‐nitrophenyl‐(2‐phenyl)‐propanoate (pNPP) with high catalytic efficiency. AlleyCatE was created by introducing a single‐histidine residue (His144) into a hydrophobic pocket of calmodulin. In this work, we explore the determinants of catalytic properties of AlleyCatE. We obtained the pKa value of the catalytic histidine using experimental measurements by NMR and pH rate profile and compared these values to those predicted from electrostatics pKa calculations (from both empirical and continuum electrostatics calculations). Surprisingly, the pKa value of the catalytic histidine inside the hydrophobic pocket of calmodulin is elevated as compared to the model compound pKa value of this residue in water. We determined that a short‐range favorable interaction with Glu127 contributes to the elevated pKa of His144. We have rationally modulated local electrostatic potential in AlleyCatE to decrease the pKa of its active nucleophile, His144, by 0.7 units. As a direct result of the decrease in the His144 pKa value, catalytic efficiency of the enzyme increased by 45% at pH 6. This work shows that a series of simple NMR experiments that can be performed using low field spectrometers, combined with straightforward computational analysis, provide rapid and accurate guidance to rationally improve catalytic efficiency of histidine‐promoted catalysis. Proteins 2017; 85:1656–1665. © 2017 Wiley Periodicals, Inc. 相似文献
59.
K. Georgieva F. Rapparini G. Bertazza G. Mihailova É. Sárvári Á. Solti Á. Keresztes 《Protoplasma》2017,254(1):193-201
Haberlea rhodopensis belongs to the small group of resurrection plants having the unique ability to survive desiccation to air dry state retaining most of its chlorophyll content and then resume normal function upon rehydration. It prefers the shady valleys and northward facing slopes of limestone ridges in mountain zones with high average humidity. Nevertheless, it can be found rarely on rocks directly exposed to the sunlight, without the coverage of the canopy. In the present study, we follow the alterations in the subcellular organization of mesophyll cells and sugar metabolism upon desiccation of shade and sun H. rhodopensis plants. Composition and content of soluble carbohydrates during desiccation and rehydration were different in plants grown below the trees or on the sunny rocks. Sucrose, however, was dominating in both ecotypes. The amount of starch grains in chloroplasts was inversely related to that of sugars. Concomitantly with these changes, the number of vacuoles was multiplied in the cells. This can be explained by the development of small (secondary) vacuoles peripherally in the cytoplasm, rather than by the fragmentation of the single vacuole, proposed earlier in the literature. Accordingly, the centripetal movement of chloroplasts and other organelles may be a result of the dynamic changes in the vacuolar system. Upon rehydration, the inner vacuoles enlarged and the organelles returned to their normal position. 相似文献