Biochimica et Biophysica Acta (BBA) - Biophysics including Photosynthesis最新文献

Analysis of chromatophore suspensions fractionated from Rhodospirillum rubrum indicated that the diphenylamine did not interfere with the cellular synthesis of bacteriochloropyll (absorption at 775 mμ in acetone-methanol). Diquat, on the other hand, interfered with the synthesis of both bacteriochlorophyll within chromatophore suspensions and the detectable Rhodospirillum heme protein of the supernatant (absorption at 435 mμ). While photoreduction of O₂ was dependent on substrates such as malate or succinate, photophosphorylation by chromatophore suspensions was mostly independent of these substrates under aerobic conditions. Under anaerobic conditions, ascorbate plus 2,6-dichlorophenolindophenol caused an “ovver-reduced” environment in which photophosphorylation was inhibited but was restored by diquat. The photophosphorylation altered by reduced 2,6-dichlorophenolindophenol and phenazine methosulfate seemed to be related to the presence of atmospheric O₂; the stimulation by phenazine methosulfate was dependent on both siccinate and O₂;

Transferrin of pooled human plasma has been found to aggregate reversibly in the presence of BrO₃⁻, IO₃⁻, SCN⁻, Cl⁻, Br⁻, I⁻, and NO₃⁻, giving weight-average sedimentation coefficients of from 5·50 S to 6·83 S compared to a normal s_20,w of 5·10 S at 0·7% concentration. The aggregation was most pronounced in the vicinity of the isoelectric points of transferrin, i.e. at pH 5·0, and was dependent on the anion, but not on the protein concentration. No aggregation was observed in the presence of acetate, formate, chloroacetate, fluoride, cacodylate and sulfate at any pH value.

• 1.

  1. Isolated pea chloroplasts were used to determine effects of temperature on photosynthetic CO₂ fixation in saturating light and high CO₂.

• 2.

  2. Increases in temperature between 5° and 30° increased the maximum rate and shortened an initial induction period. The maximum rate was not an exponential function of temperature.

• 3.

  3. Above 20°, values for the Q₁₀ were less than 2. Below 15° they were greater than 2 and increased progressively, with decreasing temperature, to values as high as 9.

• 4.

  4. The results, obtained with a purely photosynthetic system, support earlier work with intact organisms which led some investigators to conclude that photosynthesis did not obey the Arrhenius law. It is suggested that this may be a consequence of the cyclic nature of the reactions involved.

• 1.

  1. Chloroplasts were isolated from the leaves of a barley mutant which lacked chlorophyll b and compared with the chloroplasts from the normal strain which had the normal content of chlorophyll a and chlorophyll b.

• 2.

  2. Hill-reaction measurements were made with either 2,3′,6-trichlorophenol-indophenol, ferricyanide or NADP⁺ as oxidant. At a light intensity of 40 000 lux, the mutant chloroplasts were more active per mg of total chlorophyll than the normal chloroplasts, but only slightly more active per mg of chlorophyll a. Normal chloroplasts were saturated at a light intensity of about 30 000 lux whereas the mutant chloroplasts required an intensity of nearly 60 000 lux for saturation. At low light intensities (< 15 000 lux) the mutant chloroplasts were less active than the normal chloroplasts. The mutant chloroplasts were inactivated at a greater rate if allowed to stand at 0° and they were more susceptible to inhibition by 1-(p-chlorophenyl)-3,3′-dimethylurea.

• 3.

  3. Microscopic examination under phase contrast showed no significant differences in the appearance of isolated chloroplasts from the normal and mutant plants.

  The lack of chlorophyll b in the mutant was confirmed by absorption and spectrofluorimetric measurements at the temperature of liquid nitrogen. The spectrofluorimetric method was capable of detecting one molecule of chlorophyll b in the presence of 1000 molecules of chlorophyll a.

• 4.

  4. The results are discussed in relation to the function of chlorophyll b in photosynthesis.

The microfluorimetric technique to measure the intracellular oxidation-reduction state of pyridine nucleotides was applied to the isolated neuron preparation which is provided by the stretch receptor organ of the crayfish. The method allows the simultaneous recording of impulse activity. Emission spectrum of the fluorescence and the behavior of the fluorescence with continuous ultraviolet exposure were studied. Glycolytic, Krebs-cycle and respiratory inhibitors were used to investigate the cell metabolism. It was found that the fluorescence level is not altered under several conditions known to affect in other preparations the oxidized pyridine nucleotide/reduced pyridine nucleotide ratio. While Amytal and anoxia were shown, as expected, to increase the reduced pyridine nucleotides, terminal inhibitors of the cytochrome chain were ineffective. Sustained impulse activity did not alter the fluorescence level although the O₂ uptake is increased.

The exchange of peptide hydrogens with deuterium was followed by measuring the decrease of the amide II band at 1542 cm⁻¹ for heavy meromyosin.

Heavy meromyosin contains a relatively large number of slowly exchanging peptide hydrogens which decreases with increasing pH in the pH range 5.5–10.8.

The mechanism of the hydrogen isotope exchange between protein and solvent water is described in terms of HVIDT's model, where rapid equilibrium between a closed and an open molecular conformation is assumed and where only the open form is expected to exchange.

• 1.

  1. Possible cation accumulation by microsomal (Na⁺ + K⁺)-activated, ouabain-sensitive ATPase was examined by an electron microscopical method.

• 2.

  2. Densitometry measurements of membrane opacity were performed on the electron micrograph plates obtained after incubation of the ATPase preparation under a variety of experimental conditions.

• 3.

  3. To aid visualization of possible cation accumulation, the more electron opaque Cs⁺ was substituted for K⁺ in the incubation system of many experiments.

• 4.

  4. Increase in membrane density of the microsomal ATPase was observed in the presence of sodium and caesium only when ATP hydrolysis was inhibited by ouabain.

• 5.

  5. This phenomenon was not observed when a ouabain-insensitive mitochondrial ATPase system was examined.

• 6.

  6. This increase in density is interpreted as selective Cs⁺ accumulation by the microsomal enzyme membrane fragments.

• 7.

  7. The significance of these results is discussed in terms of reaction mechanism for (Na⁺ + K⁺)-activated ATPase.

• 1.

  1. The visible and near-ultraviolet optical absorption and optical rotary dispersion spectra of Chenopodium album plastocyanin were examined. Cotton effects were observed for the optical peaks in this region indicating the asymmetry of the copper chromophoric site.

• 2.

  2. Electron paramagnetic resonance spectra showed that the two copper atoms in the protein are divalent and both are in equivalent sites.

• 3.

  3. Proton relaxation rate studies showed that the copper is not on the surface of the molecule.

Photoreducibility by isolated spinach chloroplasts of 1,4-benzoquinone, tetrachloro-p-benzoquinone, 2,3-dichloro; 2-chloro-3-amino; 2-methyl, and non-substituted 1,4-naphthoquinones were studied together with oxygen evolution by the Hill reaction. It has been observed by a spectrophotometric method that the naphthoquinones were quantitatively photoreduced to corresponding hydroquinones under anaerobic conditions and readily reoxidized to the original naphthoquinones by molecular oxygen. The naphthoquinones showed no oxygen evolution by the Hill reaction. On the other hand, tetrachloro-p-benzoquinone and p-benzoquinone were photoreduced to hydroquinone under aerobic and anaerobic conditions, and stoichiometric oxygen evolution was observed by the Hill reaction. A possible correlation between the photoreducibility of these quinones and their phytotoxicity was discussed.