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Biomedical subjects

B Ke

Publications and source records attributed to B Ke.

At least 19 recordsLinked to original sources
PubMed1981

Energy transfer from phycobiliproteins to photosystem I in vegetative cells and heterocysts of Anabaena variabilis.

The presence of phycobilins in heterocysts of Anabaena variabilis is established on the basis of absorption and fluorescence spectroscopy. At 77 K heterocysts exhibit fluorescence emission bands at 645 and 661 nm indicative of phycocyanin and allophycocyanin, respectively. Both allophycocyanin levels and fluorescence emission at 695 nm were low in heterocysts relative to whole filaments. In situ fluorescence microscopy confirmed the presence of phycobilins in individual heterocysts, but the pigment levels varied considerably among cells. Heterocysts exhibited Photosystem I activity, as evidenced by photooxidation of P-700, but no Photosystem II activity. The quantum efficiency of phycobilins in sensitizing P-700 photooxidation was 50-70% that of chlorophyll a. Phycoibins were also effective in promoting light-dependent reduction of acetylene to ethylene. The results are discussed in terms of the role of the heterocyst in nitrogen fixation and of the significance of energy transfer from phycobilins to Photosystem I in heterocysts.

Cyanobacteria↗
PubMed1979

Oxidative inactivation of the molybdenum-iron-protein component of nitrogenase from clostridium pasteurianum.

The sensitivity of the molybdenum-iron(MoFe)-protein of Clostridium pasteurianum nitrogenase toward oxidation has been studied by determining the enzymatic activity of this component after incubating it anaerobically in ferricyanide solutions of various oxidizing strengths (as measured by their oxidation potentials). It was found that the MoFe-protein remains active at potentials up to +350 mV (vs. standard hydrogen electrode) but becomes readily inactivated at more oxidizing potentials, after a lag period, depending on the potential level and temperature. Oxidative inactivation by ferricyanide results in the release of most of the Mo, Fe and S atoms from the protein which causes the loss of the absorption bands in the visible region. The metals and sulfur could be re-incorporated by incubation in a mixture containing thiol, sulfide, molybdate, and ferric iron. The EPR spectrum of the oxidatively inactivated MoFe-protein showed that both the high- and low-field signals are readily affected. Re-incorporation of the metals and sulfur into the "bleached" protein produced an EPR spectrum similar to that of the air-inactivated protein. Incubation of the Mo-Fe-protein with mersalyl abolished its enzymic activity. The difference spectrum before and after mersalyl treatment resembles that of the soluble spinach ferredoxin.

Clostridium↗
PubMed1977

Electrochemical and spectro-kinetic evidence for an intermediate electron acceptor in photosystem I.

Absorption changes accompanying light-induced P-700 formation and its decay in the dark at 15 K in Photosystem-I particles poised at various redox potentials have been examined. In unpoised samples, the light-induced absorption change is practically irreversible. At increasingly negative potentials, an increasing fraction of the absorption change, proportional to the fraction of bound iron-sulfur protein chemically reduced, becomes reversible, and the titration curve has a midpoint potential of --530 mV (vs. normal hydrogen electrode). At --66 mV, the P-700 absorption change is 97% reversible. The total P-700-signal amplitude decreases over the same potential span and levels off at about 43% (to slightly over 50% at a substantially higher excitation intensity). These results provide additional support to previous suggestions of an existence of an intermediate electron acceptor located between the primary donor, P-700, and the more stable primary electron acceptor (P-430 or bound iron-sulfur protein).

Electrochemistry↗
PubMed1976

Light-induced absorption changes in photosystem I at low temperatures.

Light-induced absorption changes associated with the primary photochemical reaction and dark relaxation in Photosystem I were measured at various low temperatures. A possible temperature-dependent long-range electron tunneling process was suggested to account for the unique temperature dependence of the dark decay process. The kinetics of the light-induced absorption changes are in good agreement with the light-induced EPR changes reported earlier (Ke, B., Sugahara, K., Shaw, E.R., Hansen, R. E., Hamilton, W. D. and Beinert, H. (1974) Biochim, Biophys. Acta 368, 401--408) for the same Photosystem I subchloroplast fragment at comparable temperatures. All absorption changes between 400 and 725 nm at 86degreesK have identical kinetics. The light-minus-dark difference spectrum is very similar to that of P-700 at room temperature, with an additional prominent positive change at 690 nm. Possible contributions by P-430 to the blue and red spectral changes were discussed. It was demonstrated that the intensity of the measuring beam has a drastic effect on the light-induced absorption changes of Photosystem I at low temperatures. Various pretreatments of the Photosystem I fragments such as those that photochemically (or chemically) oxidize the primary donor or photoreduce the primary acceptor abolish the subsequent photochemical reaction. Continuous illumination of the Photosystem I fragments before and during freezing has the same effect. In the temperature range of --20 to --60degreesC, an unusual counter absorption change as well as a counter EPR change were observed.

2,6-Dichloroindophenol↗
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↗
PubMed1975

Further purification of "Triton subchloroplast fraction I" (TSF-I particles). Isolation of a cytochrome-free high-P-700 particle and a complex containing cytochromes f and b6, plastocyanin and iron-sulfur protein(s).

The "Triton Subchloroplast Fraction I" or "TSF-I particles" can be further fractionated into a cytochrome fraction and a P-700-containing fraction essentially free of cytochromes. The cytochrome complex contains cytochromes f and b6 in approx. equimolar amounts, and, in addition, also plastocyanin and one iron-sulfur protein, all in the bound state. Bound plastocyanin was characterized by EPR spectroscopy. The EPR spectrum of the bound iron-sulfur protein resembles that previously detected in Phostosystem I particles under highly reducing conditions at lower than -560 mV. The redox potential of P-700 in the cytochrome-free high-P-700 particles was measured to be +468 mV; those of cytochromes f and b6 are +345 and -140 mV, respectively. Among the four components present in the complex, only cytochrome f can be coupled to a Photosystem I particle and undergoes photooxidation. This coupled photooxidation is totoally inhibited by KCN and only partially inhibited by HgCl2. The similarity of the complex containing cytochromes f and b6, plastocyanin, and an iron-sulfur protein to complexes III and IV of the mitochondrial respiratory redox chain and a possible involvement of the complex in cyclic photophosphorylation are noted and discussed.

Binding Sites↗