102,048 research outputs found
Effects of cations on the adhesion between membrane vesicles obtained by digitonin fractionation of spinach chloroplasts.
No full textThe heavy fraction obtained by digitonin treatment of stacked spinach chloroplasts, suspended in media with different ionic composition, was examined by electron microscopy. In the presence of 5 mM MgCl2 the thylakoid fragments adhere to one another in a ‘stacked configuration,’ while, in the presence of 10 mM NaCl, mainly only single ‘unstacked’ vesicles are present, which, upon addition of 5 mM MgCl2, completely revert to the stacked configuration. As previously reported (Chow, W.S. and Barber, J. (1980) Biochim. Biophys. Acta 593, 149–157), no difference in fractionation of chlorophyll between light and heavy fractions was seen after a second digitonin treatment of this fraction suspended in media containing different cation concentrations. From these results it was concluded: (1) that for the unstacking process the movement of proteins or complexes from the stromal to the granal lamellae is not required. Upon lowering the screening by cations of the surface negative charges, the membranes separate from one another; (2) that, under these conditions, as in others (Jennings, R.C., Gerola, P.D., Garlaschi, F.M. and Forti, G. (1980) FEBS Lett. 115, 39–42), digitonin fractionation is not a tool to investigate the degree of membrane stacking
Photoinhibition in vivo and in vitro involves weakly coupled chlorophyll-protein complexes
No full textIn the present study the analysis of the relation between the excited state population in the photosystem 11 (PSII) antenna and photoinactivation has been extended from an in vitro system, isolated thylakoids, to an in vivo system, Chlamydomonas reinhardtii cells. The results indicate that the excited state quenching by an added singlet quencher induces maximal protection against photoinhibition of about 30% of that expected on the basis of the observed light intensity-treatment time reciprocity rule. Similar results, obtained previously with thylakoids, have been interpreted in terms of damaged or incorrectly assembled complexes that play an important role in photoinhibition in the thylakoid membranes (Santabarbara, S., K. Neverov, F. M. Garlaschi, G. Zucchelli and R. C. Jennings [2001] Involvement of uncoupled antenna chlorophylls in photoinhibition in thylakoids. FEBS Lett. 491, 109-113.). In an attempt to better define this aspect, the photoinhibition action spectra were determined for mutant barley thylakoids, lacking the chlorophyll (Chl) a-b complexes of the outer antenna, and for its wild type. The results indicate that in both systems the action spectra are significantly blueshifted (2-4 nm) and are broader than the PSII absorption in the membranes. These data are interpreted in terms of a heterogeneous population of outer and inner antenna pigment-protein complexes that contain significant levels of uncoupled Chl
The influence of proton induced grana formation on partial electron transport reactions in chloroplasts
No full textPrimary lymphoma of the mandible with diffuse widening of the mandibular canal: report of a case
No full textStudies on the kinetics of cation-associated fluorescence changes in chloroplast membranes.
No full textHere we present an analysis of the kinetics of cation effects on chlorophyll fluorescence yield in an attempt to distinguish between these various possibilities.
The main finding we report is that the fluorescence decline which occurs on EDTA addition to the chloroplast membranes incubated in the presence of Mg 2÷ can be explained adequately by second-order reaction kinetics involving two different substrates in
an environment in which one of the substrates is present in two kinetically distinguishable 'subpopulations'
Reply to “Commentary on Photosynthesis and Negative Entropy Production by Jennings and coworkers” by J. Lavergne
No full textAbstractIt is argued that the chemical potential analogy does not provide useful information on the thermodynamics of photosystems, as the thermodynamic efficiency of an absorbed quantum is not considered. Instead, the approach based on either entropy balance or entropy flux considerations does provide this information. At high thermodynamic efficiencies, primary photochemistry can, in principle, violate the Second Law of Thermodynamics
Excited State Trapping and the Stepanov Relation with Reference to Photosystem I
No full textAbstractIt has been previously demonstrated that the Stepanov equation provides a rather good description of the absorption/fluorescence spectra in Photosystem I, even though excited state equilibration is not rapid with respect to the excited state decay. In the present article this apparent contradiction is examined analytically for two-state systems and numerically for many-state systems. It is demonstrated that, in the special case of the trapping process being associated with the initially populated state, neither very rapid excited state equilibration nor a transfer equilibrium, which approximates a true Boltzmann distribution, are prerequisites to obtaining a very close approximation to a correct Stepanov result. This interesting conclusion is discussed in terms of plant Photosystem I (PSI-200). It is concluded that whereas, in compartmental modeling, photochemical trapping may be formally associated with the bulk antenna pigments due to the strong energy coupling between them and the trap pigments, this is not the case for the red spectral forms
- …
