Biochimica et Biophysica Acta (BBA) - Specialized Section on Biophysical Subjects最新文献

Studies mutants and isolated molecular structures demonstrate that the two haem proteins—cytochrome c (552, Euglena) and cytiochrome b (561, Euglena)—are functionally localized in the choloplasts. Two others—cytochrome type c (556, Euglena) and cytochrome type a (605, Euglena)—appear to be associated with the respiratory system.

Data obatined by kinetic analyses of composition during various phases of chloroplast development indicate that functional units in the chlotoplast are built containing constant ratios of chlorophyll to the photosynthetic cytochromes (350 chlorophyll molecules for each cytochrome).

The reducing moiety of the photosynthetic cycle, resulting in TPN⁺ reduction, and the oxidizing moiety (cytochromes), resulting in the main part of ATP production, were excited by separate light reactions and showed different action spectra. The two light reactions were also characterized by specific changes in the absorption spectra of the pigments. The reducing system was more sensitive to blue-green light, oxidized carotenoids (negative band at 500 mμ) and reduced an initial reductant. The oxidizing system was specifically sensitive to red light, oxidized the cytochrome system and reduced the pigments via chlorophyll and unknown factors showing negative bands at 640 mμ. The action spectra showed a multilateral linkage between pigments and enzyme systems and considerable activity also in green at higher light intensities. It is suggested that the enzyme systems together form a balancing steady state, which operates also in the dark and is sensitive to variations in the concentrations of O₂ and various substrates. The site of O₂-production (photolysis of H₂O) is probably at the junction of th two redox systems, viz. at the autoxidable cytochrome, b₃ and flavoprotein. Its action spectrum showed characteristics of both the reducing and oxidizing systems. The action spectra are influenced by light scattering.

The Hill-reaction activity of pigment-containing particles prepared from the blue-green alga, Anabaena variabilis, has been studied. Depending on the medium used for cell breakage and particle isolation, particles are obtained which have either largely lost or partially retained the accessory photosynthetic pigment, pycocyanin. Both types of particles show Hill-reaction activity to a variety to electron acceptors at rates which compare favorably to those seen with higher-plant chloroplasts. Only at limiting light intensities does the presence of phycocyanin in the particle appear to make a difference in the rate of the Hill reaction. The Hill-reaction activity of these preparations is unique in showing a marked stimulation by Mg²⁺.

Respiratory activity of chromatophores of Rhodospirillum rubrum, as measured by the O₂ uptake, was almost doubled by illumination. Succinoxidase activity of chromatophores was inhibited considerably by o-phenanthroline but not inhibited by KCN either in the dark or light. The aerobic oxidation of p-phenylenediamine in the dark was not inhibited by o-phenanthroline but was completely inhibited by KCN, whereas the oxidation in the light was sensitive to o-phenanthroline but insensitive to KCN. o-Phenanthroline also inhibited other CN⁻-insensitive reactions in chromatophores, such as photooxidation of reduced cytochrome c₂ and the dark-anaerobic oxidation of NADH coupled to the reduction of fumarate. Antimycin A did not inhibit the succinoxidase activity in the dark, but significantly inhibited the activity in the light. Succinate-cytochrome c₂ reductase activity was sensitive to antimycin A but insensitive to o-phenanthroline, whereas NADH-cytochrome c₂ reductase activity was insensitive to antimycin A but sensitive to o-phenanthroline.

The terminal oxidation system in chromatophores is discussed with particular reference to the marked stimulation of O₂ uptake by illumination.

The absorption spectrum of spinach quantasomes is compared with those of whole chloroplasts and intact leaves. Using the scattered-transmission technique, it is shown that the absorption maximum at 678.5 mμ in spinach leaves is not shifted in the preparation of isolated chloroplasts or by sonication and separation of small quantasome aggregates.

The effects of several organic compounds and surface-active agents on the absorption spectra, chlorophyll fluorescence and Hill-reaction activity of quantasomes fall into two general classes. Added acetone, methanol, urea or sodium dodecyl sulfate induce a loss in Hill activity at appreciably lower concentrations than are required to give a pronounced fluorescence increase or blue shift in the absorption maximum at 678 mμ. On the other hand, quantasomes treated with Triton X-100 retain Hill activity at higher concentrations of the non-ionic detergent than are necessary to produce pronounced absorption and fluorescence changes. The principal conclusions reached are: (1) the position of the chlorophyll maximum in the red is not a sensitive measure of the ability of photosynthetic materials to carry out the Hill reaction, (2) energy diverted from normal photochemical pathways does not in general immediately appear as enhanced fluorescence, and (3) detergent concentrations comparable to the chlorophyll concentrations of quantasome aggregates are capable of profound effects on physical properties.