Photosynthetic bacteria kinetics

In a chemostat and biostat or turbidostat, even with differences in the supply of nutrients and/or fresh media, constant cell density is obtained. The utilisation of substrate and the kinetic expressions for all the fermentation vessels are quite similar. It is possibile to have slight differences in the kinetic constants and the specific rate constants.3,4 Figure 5.9 shows a turbidostat with light sources. The system can be adapted for photosynthetic bacteria. 

Zero field splitting (zfs) values in photoexcited triplets of primary donor bacteriochlorophyll a in photosynthetic bacteria are much lower than those found for vitro BChla triplets. There is a pronounced difference in kinetics of population and depopulation of the triplet sublevels as well. The differences have been attributed to the effect of BChla dimerization and it is now generally accepted that the primary electron donor in photosynthetic bacteria consists of a BChla dimer (special pair)(l- ). 

Woodbury, N. W., M. Becker, D. Middendorf, and W. W. Parson, Picosecond kinetics of the initial photochemical electron transfer reaction in bacterial photosynthetic reaction centers. Biochem. 24 7516, 1985. Fast spectrophotometric techniques are used to follow the initial steps in reaction centers purified from photosynthetic bacteria. 

Kinetics of Electron Transfer in the Reaction Centre Proteins from Photosynthetic Bacteria... 

Everybody knows of the spectacular success of unravelling the structure and kinetics of the photosynthetic bacteria, rhodopseudomonas sphaeroides and viridis the structure by Deisenhoffer, Huber and Michel (Deisenhofer et al., 1984) following the isolation and crystallisation by Michel (Michel, 1982) and the picosecond kinetics (which came first) by Rockley, Windsor, Cogdell and Parson (Rockley et al., 1975) and also by Dutton, Rentzepis, Netzel et al. (Netzel et al., 1977). 

Woodbury, N. W., and Allen, J. P., 1995, The pathway, kinetics and thermodynamics of electron transfer in wild type and mutant hacterial reaction centers of purple nonsulfur hacteria. In Anoxygenic Photosynthetic Bacteria, (R. E. Blankenship, M. T. Madigan, and C. E. Bauer, eds.) pp. 5279557, Kluwer Academic Publishers, Dordrecht, The Netherlands. 

In purple photosynthetic bacteria, and specifically in Rps. sphaeroides and Rps. capsulata, three cytochromes of b type have been identified by means of redox titration, in the dark, of isolated chromatophores [116]. They are characterized by midpoint potentials at pH = 7.0 equal to 0.155, 0.050 and -0.090 V (in Rps. sphaeroides)-, the of the 0.050 V species is pH dependent ( — 60 mV per pH unit) [116,117]. The presence of a cytochrome cc in these organisms, interfering spectrally with cytochrome b, makes the situation unclear as far as the existence of cyt. b E j = 0.155 V) is concerned [118]. The two other cytochromes E = 0.050 and — 0.090 V) have also been resolved kinetically in studies on the photosynthetic electron transport and on the basis of their spectral characteristics (band at 561 nm and a spht bands at 558 and 556 nm, respectively these two cytochromes will be referred to as 6-561 and 6-566 in the following) [119]. 

A second bound form of cytochrome c is an integral part of the oxidoreductase complexes. Cytochrome c, present in photosynthetic bacteria has been distinguished from cyt. C2 (the soluble electron carrier) both thermodynamically and kinetically [121,122]. It is present in the isolated oxidoreductase with a stoicheiometry of one per two cytochromes of b type, and it is associated with the 34000 Da subunit. According to kinetic evidence this cytochrome acts as immediate electron donor to cyt. C2 and electron acceptor from the high potential Fe-S protein [122]. The midpoint potential of cyt. c, is 0.285 V at pH 7 [121,122]. 

The location of cytochrome C2 in the periplasmic space of purple photosynthetic bacteria has been demonstrated directly by its prompt release following the preparation of sphaeroplasts, and by its accessibility to antibodies in these preparations [220]. Cytochromes c are oxidized in single turnover experiments with a biphasic kinetics (<1 2 and 200-400 /is) this pattern has been interpreted as due to the presence in chromatophores of both cyt. Cj and C2, which are oxidized in series [122]. 

Results from additional picosecond kinetic measurements of the photochemical and electron-transfer reactions in photosynthetic bacteria also gave support to the notion of the existence of an intermediary electron acceptor. This can best be illustrated with the kinetic studies of Kaufmann, Dutton, Netzel, Leigh and Rentzepis on the involvement of BO as a transient intermediary electron acceptor in photosynthetic bacteria. When Q is functional, i.e., Q is present in the oxidized state [see Fig. 1], flash illumination would be expected to produce first the [P BO"]-Q-state followed by the [P BO] Q -state. Examination of this reaction by picosecond spectroscopy revealed both the time it takes for electron donation from P to BO and the lifetime of BO , i.e., the time it takes for BO to transfer an electron to Q. 

Femtosecond kinetics of photochemical charge separation in photosynthetic bacteria at low temperatures (25 K) was studied by Lautwasser, Finkele, Scheer and Zinth using Rb. sphaeroides RCs depleted of quinones. Fig. 9 (C, a) shows the initial formation of P at 920 nm followed by a very rapid relaxation with a Ti of 1.4 0.3 ps. At 794 nm and 25 K, the absorption increases very rapidly to a maximum in about 0.1 and then decays to a minimum at tD 0.5 ps. This is followed by a slow rise and a plateau after 5 ps. The early rapid-decay component with a time constant of 0.3 0.15 ps appears to be the counterpart of the 0.9-ps component at room temperature. The data points in Fig. 9 (C, b) can be fitted by a model with three time constants, namely 0.3ps, l.Aps and 1 ns. 

As in the case of the purple photosynthetic bacteria, the more stable electron acceptor of green filamentous bacteria was first detected using instrumentation with millisecond-time resolution and so the rise and decay kinetics of any earlier electron acceptor(s) would be too fast to be detected. The detection of any earlier electron acceptor would require greater time resolution, such as afforded by picosecond spectroscopy. As a framework for further discussion we write the sequence of the primary photochemical and electron-transfer reactions in green filamentous bacteria as follows ... 

EFFICffiNCY AND KINETICS OF ENERGY TRANSFER IN CHLOROSOME ANTENNAS FROM GREEN PHOTOSYNTHETIC BACTERIA... 

Efficiency and Kinetics of Energy Transfer in Chlorosome Antennas from Green Photosynthetic Bacteria 17... 

The photophysical and electron transfer properties of bacteriochlorophylls (Bchl) and bacteriopheophytins (Bpheo) found in the reaction centers of photosynthetic bacteria have been directly associated with the mechanism of charge separation which underlies photosynthesis [1]. The appearance of the Bpheo anion (Bpheo ) within 3-5 ps after excitation of the special pair of Bchl (P) is well documented from transient absorption spectroscopy [2-4]. The 200 ps lifetime of Bpheo which is primarily determined by the electron transfer process to a quinone also has been established by picosecond changes in absorption [5,6], Thus, the general kinetic time scale for the primary processes in bacterial photosynthesis has been determined by the transient differences in electronic state properties. 

Z. D. Popovic, G. J. Kovacs, P. S. Vincett, G. Alegria, and P. L. Dutton, Electric field dependence of recombination kinetics in reaction centers of photosynthetic bacteria, Chem. Phys. 110 227 (1986). 

Sundstrom, V. and GrondeUe van, R., Kinetics of excitation transfer and trapping in purple bacteria, in Anoxygenic Photosynthetic Bacteria, Blankenship, R., Madigan, M.T., and Bauer, C.E., Eds.,... 

Rhodospririllum rubrum is the most exhaustively studied of the purple nonsulfur bacteria. The photosynthetic apparatus is located in extensive infolded membrane vesicles called chromatophores. Cytochromes C2, cd, and 1)557.5 have all been found to be associated with the chromatophores (371), with C2 being the major component. Several lines of evidence, including fast kinetics following the excitation of the baeteriochlorophyll photocenter by laser flash, have suggested the scheme shown in Fig. 29, where cytochrome Cj is the immediate source of electrons to the electron-... 

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