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Biomedical subjects

J M Olson

Publications and source records attributed to J M Olson.

At least 109 records · Page 6Linked to original sources
PubMed1981

Evolution of photosynthetic reaction centers.

The common ancestor of all photosynthetic prokaryotes and organelles contained chlorophyll (Chl) a. All green and purple photosynthetic bacteria descended from a common bacteriochlorophyll (Bchl) a-containing ancestor which diverged from the Chl a line. Separate PS-I and PS-II reaction centers may have evolved before the appearance of Bchl a. When the transition to Bchl a occurred, the resultant organism contained two types of reaction center, "PS-I" and "PS-II." One line of development eliminated "PS-II" and evolved into the green bacteria. The other line eliminated "PS-I" and became the purple bacteria. In the Chl a-containing organisms the evolution of PS-II continued until oxygen evolution was achieved.

Bacteria↗
PubMed1980

Chlorophyll organization in green photosynthetic bacteria.

Light-harvesting BChl c, d or e is thought to be located inside the rod elements which fill the chlorosome appressed to the inside of tbe cytoplasmic membrane of green photosynthetic bacteria. BChl a is known to be a part of BChl a-protein which forms a crystal-line baseplate between the rod elements in the chlorosome and the inside of the cytoplasmic membrane. Reaction-center complexes are most probably buried under the baseplate inside the membrane. Energy transfer is from BChl c, d or e in the rod elements to BChl a in the baseplate and then to BChl a in the reaction-center complexes. The rod elements in green sulfur bacteria are thought to be composed of approx. 15-kdalton protein subunits, each associated with 12-14 BChl c, d or e molecules. Six subunits would be required to form a 10-nm ring, and about 35 rings would be necessary to form a 100-nm rod element. The baseplate appears to be a two-dimensional crystal (trigonal space group P31) of BChl a-protein trimers with the 3(1) screw axis tilted 25 degrees out of the plane membrane. The reaction-center complex is thought to be made up of a 100-kdalton carotenoid reaction-center core and five 50-kdalton subunits, each containing seven BChl a molecules. Each reaction-center complex is apparently linked directly to two BChl a-protein trimers in the baseplate. The reaction centers in green sulfur bacteria may be of one type (containing P-840), or of two types (containing P-830 or P-842). In filamentous gliding bacteria the reaction centers appear to contain only P-865. The number of BChl a molecules in these reaction centers is not known, but is assumed to be at least two.

Amino Acids↗
PubMed1980

Seven-fold exciton splitting of the 810-nm band in bacteriochlorophyll A-proteins from green photosynthetic bacteria.

We report comparative absorbance and fourth derivative absorbance spectra of two different bacteriochlorophyll a-proteins at 5 K in each of two different cryogenic solvent mixtures. In previous studies at 5 K each protein was observed in only one of these mixtures (not the same one). For the protein from Prosthecochloris aestuarii strain 2K, whose structure is known, the solvent effect is relatively small; for the protein from Chlorobium limicola f. sp. thiosulfatophilum strain 6230 (Tassajara), the effect is much more pronounced. From these results together with earlier results at 300 K, we conclude there may be slight conformational differences of the Prosthecochloris protein between the crystalline form used for X-ray diffraction studies and that in a cryogenic solvent. By comparing spectral features of the two proteins in the same solvent, we are able for the first time to assign all seven of the expected exciton levels in each protein. These occur at 793, 801, 806, 810, 814, 819, and 825 nm in the Prosthecochloris protein, and at 793, 802, 806, 810, 816, 820, and 823 nm in the Chlorobium protein.

Bacteria↗
PubMed1976

The amino acid sequences of the cytochromes c-555 from two green sulphur bacteria of the genus Chlorobium.

Amino acid seauences are proposed for the cytochromes c-555 from Chlorobium thiosulphatophilum and from the Chlorobium limicola component of "Chloropseudomonas ethylica 2K". Each is a sincle polypeptide chain, the former of 86, the latter of 99 residues, and, when aligned so as to give the best match, 47 residues are common to the two sequences. The sequences show some resemblance to those of cytochromes c5 and f. The bacteriochlorophyll a-proteins were also isolated and purified, and their amino acid compositions compared (see the Appendix). There are significant differences in the compositions, but not as great as those found for the cytochromes c-555. The significance of these observations for the taxonomy of the Chlorobiaceae and for the further development of the comparative biochemistry of cytochrome c is discussed. Detailed evidence for the sequences of the cytochromes c-555 has been deposited as Supplementary Publication SUP 50073 (36 pages) at the British Library Lending Division, Boston Spa, Wetherby, West Yorkshire LS23 7BQ, U.K., from whom copies may be obtained on the terms given in Biochem. J. (1976) 153, 5.

Amino Acid Sequence↗
PubMed1976

An enriched reaction center preparation from green photosynthetic bacteria.

Bacteriochlorophyll a reaction-center complex I from Chlorobium limicola f. thiosulfatophilum 6230 (Tassajara) was incubated in 2 M guanidine - HCl and then chromatographed on cross-linked dextran or agarose gel. Two principal components were separated: a larger component with photochemical activity (bacteriochlorophyll a reaction-center complex II) and a smaller component without activity (bacteriochlorophyll a protein). Complex II contains carotenoid, bacteriochlorophyll a, reaction center(s), and cytochromes b and c, but lacks the well characterized bacteriochlorophyll a protein contained in Complex I. Complex II carries out a light-induced reduction of cytochrome b along with an oxidation of cytochrome c.

Ascorbic Acid↗
PubMed1976

Exciton interaction among chlorophyll molecules in bacteriochlorophyllaproteins and bacteriochlorophyllareaction center complexes from green bacteria.

Absorption and CD spectra of bacteriochlorophyll a proteins and bacteriochlorophyll a reaction center complexes from two strains of Chlorobium limicola were recorded at 77 degrees K. Visual inspection showed that the Qy-band of chlorophyll in either protein was split into at least five components. Analysis of the spectra in terms of asymmetric Gaussian component pairs by means of computer program GAMET showed that six components are necessary to fit the spectra from strain 2K. These six components are ascribed to an exciton interaction between the seven bacteriochlorophyll a molecules in each subunit. The clear difference between the exciton splitting in the two bacteriochlorophyll a proteins shows that the arrangement of the chlorophyll molecules in each subunit must be slightly different. The spectra for the bacteriochlorophyll a reaction center complexes have a component at 834 nm (absorption) and 832 nm (CD) which does not appear in the spectra of the bacteriochlorophyll a proteins. The new component is ascribed to a reaction center complex which is combined with bacteriochlorophyll a proteins to form the bacteriochlorophyll a reaction center complex. The complete absorption (or CD) spectrum for a given bacteriochlorophyll a reaction center complex can be described to a first approximation in terms of the absorption (or CD) spectrum for the corresponding bacteriochlorophyll a protein plus the new component ascribed to the reaction center complex.

Bacteria↗
PubMed1976

Some thermodynamic and kinetic properties of the primary photochemical reactants in a complex from a green photosynthetic bacterium.

We have examined the bacteriochlorophyll reaction-center complex of Chlorobium limicola f. thiosulfatophilum, strain Tassajara. Our results indicate that the midpoint potential of the primary electron donor bacteriochlorophyll of the reaction center is +250 mV at pH 6.8, while that of cytochrome c-553 is +165 mV. There are two cytochrome c-553 hemes per reaction center, and the light-induced oxidation of each is biphasic (t1/2 of less than 5 mus and approximately 50 mus). We belive that this indicates a two state equilibrium with each cytochrome heme being either close to, or a little removed from, the reaction-center bacteriochlorophyll. We have also titrated the primary electron acceptor of the reaction center. Its equilibrium midpoint potential at pH 6.8 is below -450 mV. This is very much lower than the previous estimate for green bacteria, and also substantially lower than values obtained for purple bacteria. Such a low-potential primary acceptor would be thermodynamically capable of direct reduction of NAD+ via ferredoxin in a manner analagous to photosystem I in chloroplasts and blue-green algae.

Bacteria↗