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Biomedical subjects

G Renger

Publications and source records attributed to G Renger.

At least 91 records · Page 5Linked to original sources
PubMed1979

Studies on the proton transport at system II in trypsin-treated spinach chloroplasts.

The proton transport coupled with the DCMU-insensitive oxygen evolution mediated by K3[Fe(CN)6] in trypsin-treated chloroplasts (Renger, G. (1976) FEBS Lett. 69, 225--230) has been investigated with the aid of the pH indicator bromcresol purple. It was found that (1) the proton uptake from the outer aqueous phase observed in normal chloroplasts is completely suppressed by mild trypsin treatment; (2) a rather slow proton release into the external phase is detected which is insensitive to DCMU; (3) in the presence of DCMU, the extent of the proton release depends on the incubation time with trypsin in a similar manner as the average oxygen yield per flash. The results are interpreted by the assumption, that: (i) the reduced primary electron acceptor of System II, X 320-, does not become protonated, and (ii) the external acidification is caused by a passive efflux of protons, which are released by the watersplitting enzyme system Y into the inner phase of the thylakoids. The pK value of X 320- in trypsinated chloroplasts is estimated to be below 4.5. A possible pK shift caused by a modification of the proteinaceous barrier, which earlier (Renger, G. (1976) Biochim. Biophys. Acta 440, 287--300) was postulated to cover up the primary electron acceptor X 320, is discussed. Furthermore, the watersplitting enzyme system Y is inferred to be sensitive to deletereous attack from the outer aqueous phase mainly by secondary structural effects. Trypsination does not change the direction of the proton release in system Y.

Chloroplasts↗
PubMed1977

Further evidence for dissipative energy migration via triplet states in photosynthesis. The protective mechanism of carotenoids in Rhodopseudomonas spheroides chromatophores.

The protection action of carotenoids against irreversible photodestruction was discovered in photosynthetic bacteria by Stanieda and coworkers. In green plant material it was found by Wolff and Witt (1969) Z. Naturforsch, 24b, 1031-1037 and (1972) Proc. 2nd. Int. Congr. Photosynthesis Res. Stresa (Forti, G., Avron, M. and Melandri, A., eds.), Vol. 2, pp. 931-936, Dr. W. Junk, N. V. Publ. The Hague) that the formation of special carotenoid triplet states (via very rapid energy transfer from excited chlorophylls) and their fast radiationless decay in tau1/2 approximately 3 microns is at least one mechanism for the protective action of carotenoids to irreversible photooxidation of the chlorophylls. Hence, it is anticipated that the same mechanism might be realized also in bacteria. The present study gives evidence for such a "triplet valve" to be established also in bacteria. This conclusion was derived from the following observations: 1. The light-induced difference spectrum shows a bleaching of a carotenoid at three characteristic wavelength between 400 and 500 nm. A positive peak around 533 nm indicates the formation of a carotenoid triplet state. 2. The absorption changes can be induced by red light which excites only bacteriochlorophyll. This indicates an energy transfer from bacteriochlorophyll to carotenoids. 3. The light-induced carotenoid triplets decay radiationless in 3 microns in air-saturated aqueous suspensions of the chromatophores. 4. The carotenoid triplet formation occurs only at actinic flash intensities where the photosynthesis becomes saturated. 5. Addition of dithionite, which blocks photosynthesis, markedly increases the extent of carotenoid triplet formation. The different types of exciton migration within the photosynthetic unit are discussed, especially the routes leading to the dissipation of excess excitation energy.

Bacterial Chromatophores↗
PubMed1976

Studies on the nature of the inhibitory effect of trypsin on the photosynthetic electron transport of system II in spinach chloroplasts.

The effect of trypsin on the photosynthetic electron transport of spinach chloroplasts has been investigated by measurements of the flash-induced absorption changes, indicating chlorophyll a1 at 703 nm, chlorophyll aII at 690 nm and at 515 nm via electrochromism the electrical potential gradient across the thylakoid membrane, respectively, and of the fluorescence induction caused by moderate actinic light. It was found: (1) In the presence of benzyl viologen as electron acceptor and with water as natural electron donor trypsin, incubation leads to a complete suppression of the absorption changes of the electrochromic effect and of chlorophyll aI and chlorophyll aII. (2) Addition of System I electron donors (N-methylphenazonium sulfate plus ascorbate or 2,6-dichlorophenolindphenol plus ascorbate) fully restores the chlorophyll aI photoreaction, whereas the initial amplitude of the electrochromic absorption change at 515 nm amounts about 50% of the control value without trypsin. The chlorophyll aII inhibition remains uneffected by System I electron donors. (3) System II electron donors (benzohydroquinone plus ascorbate or TPB) are unable to overcome the inhibition of electron transport by trypsin. (4) The fluorescence induction curve in 3-(3,4-dichlorophenyl)-1,1-dimethyl-urea-blocked chloroplasts is modified by trypsin. The level of maximal fluorescence is remarkably decreased, whereas the initial fluorescence remains constant. The rise in kinetics is slightly decelerated. From these results, it is concluded that in the linear electron transport from water to benzyl viologen, mild trypsin treatment specifically attacks System II at a site very close to the reaction center, either on the oxidizing or on the reducing side. The reaction center of System II itself is relatively stable against trypsin. Arguments are presented which argue in favor of the trypsin attack being primarily directed at the reducing side of System II.

2,6-Dichloroindophenol↗
PubMed1976

Studies on the structural and functional organization of system II of photosynthesis. The use of trypsin as a structurally selective inhibitor at the outer surface of the thylakoid membrane.

The effect of trypsin on the photosynthetic electron transport has been investigated in the presence of various electron acceptors (benzyl viologen, p-benzo-quinone, K3[Fe(CN)6]) by measurements of flash-induced oxygen evolution and of the absorption changes at 334 nm, indicating the primary electron acceptor of System II, X 320, and at 515 nm, indicating via electrochromism the electrical potential gradient across the thylakoid membrane. It was found that the effect of trypsin is strongly dependent on the nature of the electron acceptor: (1) Oxygen evolution is completely inhibited in the presence of p-benzo-quinone, but remains nearly unaffected by K3[Fe(CN)]6. (2) The initial amplitude deltaAO of the 334 nm absorption change is insensitive to trypsin in the presence of K3[Fe(CN)6], but the absorption change is abolished if benzyl viologen is used as acceptor. (3) The initial amplitude deltaAO of the 515 nm absorption change decreases by trypsin down to 50% with K3[Fe(CN)6] and is completely suppressed with benzyl viologen. (4) In trypsinated chloroplasts, the above-mentioned activities appear to be rather insensitive to 3-(3,4-dichlorophenyl)-1,1-dimethylurea, in contrast to normal chloroplasts. On the basis of these results it is inferred that the primary electron acceptor of System II, X 320, is covered by a proteinaceous component susceptible to tryptic digestion. In addition, it is postulated that this component acts as well as an allosteric protein responsible for the regulation of the electronic interaction between X 320 and the plastoquinone pool, as for the inhibitory effect of 3-(3,4-dichlorophenyl)-1,1-dimethylurea. Various other possible effects caused by the proteinaceous shield and its modification by trypsin are discussed. The present results are in complete agreement with asymmetric membrane models postulating a zig-zag arrangement of the electron transport chain with the reducing side located towards the outer phase and the oxidizing side near the inner phase of the thylakoids.

2,6-Dichloroindophenol↗
PubMed1976

The existence of a high photochemical turnover rate at the reaction centers of system II in Tris-washed chloroplasts.

In Tris-washed chloroplasts the kinetics of the primary electron acceptor X 320 of reaction center II has been investigated by fast repetitive flash spectroscopy with a time resolution of approximately 1 mus. It has been found that X 320 is reduced by a flash in less than or equal to 1 mus. The subsequent reoxidation in the dark occurs mainly by a reaction with a 100-200 mus kinetics. The light-induced difference spectrum confirms X 320 to be the reactive species. From these results it is concluded that in Tris-washed chloroplasts the reaction centers of System II are characterized by a high photochemical turnover rate mediated either via rapid direct charge recombination or via fast cyclic electron flow.

Chloroplasts↗