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S Acker

Publications and source records attributed to S Acker.

14 recordsLinked to original sources
PubMed1979

Absorption changes of P-700 reversible in milliseconds at low temperature in Triton-solubilized photosystem I particles.

Triton-solubilized Photosystem I particles from spinach chloroplasts exhibit largely reversible P-700 absorption changes over the temperature range from 4.2 K to room temperature. For anaerobic samples treated with dithionite and neutral red at pH 10 and illuminated during cooling, a brief (1 microseconds) saturating flash produces absorption changes in the long wavelength region that decay in 0.95 +/- 0.2 ms from 4.2 to 50 K. Above 80 K a faster (100 +/- 30 microseconds) component dominates in the decay process, but this disappears again above about 180 K. The major decay at temperatures above 200 K occurs in about 1 ms. The difference spectrum of these absorption changes between 500 and 900 nm closely resembles that of P-700. Using ascorbate and 2.6-dichlorophenolindophenol as the reducing system with a sample of Photosystem I particles cooled in darkness to 4.2 K, a fully reversible signal is seen upon both the first and subsequent flashes. The decay time in this case is 0.9 +/- 0.3 ms.

Chlorophyll↗
PubMed1978

Electron acceptors associated with P-700 in Triton solubilized photosystem I particles from spinach chloroplasts.

Flash-induced absorption changes of Triton-solubilized Photosystem I particles from spinach were studied under reducing and/or illumination conditions that serve to alter the state of bound electron acceptors. By monitoring the decay of P-700 following each of a train of flashes, we found that P-430 or components resembling it can hold 2 equivalents of electrons transferred upon successive illuminations. This requires the presence of a good electron donor, reduced phenazine methosulfate or neutral red, otherwise the back reaction of P-700+ with P-430 occurs in about 30 ms. If the two P-430 sites, designated Centers A and B, are first reduced by preilluminating flashes or chemically by dithionite under anaerobic conditions, then subsequent laser flashes generate a 250 microseconds back reaction of P-700+, which we associate with a more primary electron acceptor A2. In turn, when A2 is reduced by background (continuous) illumination in presence of neutral red and under strongly reducing conditions, laser flashes then produce a much faster (3 microseconds) back reaction at wavelengths characteristic of P-700. We associate this with another more primary electron acceptor, A1, which functions very close to P-700. The organization of these components probably corresponds to the sequence P-700-A1-A2-P-430[AB]. The relation of the optical components to acceptor species detected by EPR, by electron-spin polarization or in terms of peptide components of Photosystem I is discussed. Preliminary experiments with broken chloroplasts suggest that an analogous situation occurs there, as well.

Chlorophyll↗
PubMed1976

[Photosynthetic activity in the absence of CPl and CP2 pigmentary complexes (author's transl)].

Various photochemical activities were tested on chloroplasts of Zea mays that received 4 s of light every 4 h during the culture period. Photosystem I and Photosystem II were functioning, as well as the photosynthetic electron transport. These chloroplasts exhibited upon sodium dodecyl sulphate gel electrophoresis neither Complex 1 (Mr 70 000) generally associated with Photosystem I nor Complex 2 Mr 25 000) generally associated with Photosystem II. Chlorophyll is indeed attached to polypeptides of molecular weight 21 000 and 29 000. These results lead us to question the functional role of chloroplast protein-pigment complexes observed by sodium dodecyl sulphate gel electrophoresis.

Chloroplasts↗
PubMed1975

[Independence of special forms of chloeophyll a and chlorophyll holochromes].

Zea mays L. seedlings were cultivated for 10 days with submission to 4 s illumination periods interspersed with dark periods varying in length from 30 min to 6 h depending on the lot analyzed. The results show that, for the case in which the dark periods were shorter than 1 h, the relative proportions of different spectroscopic chlorophyll forms (maxima at 662, 670, 677.5, and 684 nm) were constant. For longer durations of darkness between illuminations, the relative proportion of the form Da670 increases, while that of Ca684 diminishes with the length of darkness; to a lesser extent, the relative proportion of Ca662 increases and a form Ca692 disappears. A scheme is proposed to explain the evolution of the relative proportions of the different spectral forms. The different chlorophyll holochromes present in the chloroplasts were also analysed. If the dark period was longer than 1 h, chlorophyll was associated with peptide chains of molecular weights 21 000 and 29 000. If the dark period was shorter than 1 h chlorophyll was associated with four peptide chains of molecular weights 21 000, 25 000, 29 000 and 70 000. The results taken together demonstrate that a given spectral chlorophyll a form cannot be associated with a definite chlorophyll holochrome.

Binding Sites↗
PubMed1975

Extension of cervical carcinoma to lumbar spine.

Carcinoma of the cervix is a lesion in which involvement of the spinal column is not generally considered. Two recent cases attest to the fact that this lesion may compress the lumbar vertebrae and cause paralysis, due to aorta iliac node metastases. Laminectomy with decompression, followed by radiation therapy, only temporarily alters the course of the lesion. With present technics the portals of irradiation are inadequate to prevent this lesion.

Adult↗