Measurement of the extent of electron transfer to the bacteriopheophytin in the M-subunit in reaction centers of Rhodopseudomonas viridis
- Argonne National Lab., IL (USA)
We have carried out a more stringent test for electron transfer along the M-pathway at low temperature. This has been done by directly detecting transient states generated from the trapped PH{sub L}{sup {minus}}H{sub M} state in Rps viridis reaction centers. Under these conditions the normal forward electron transfer to H{sub L} is blocked, and the yield of transient P{sup +}H{sub M}{sup {minus}} is determined with respect to the lifetime of P*. Others have measured this lifetime to be 20 ps at room temperature. This enhances the opportunity for detecting a reaction between P* and H{sub M} by 20-fold. These experiments find that transient bleaching of the P990 nm band occurs from the trapped PH{sub L}{sup {minus}}H{sub M} state on the ns time scale, with a quantum yield of 0.09 {plus minus} 0.06 compared to normal photochemistry. This measurement places an upper limit on the yield of a transient P{sup +}H{sub M}{sup {minus}} state. The measured yield and estimated lifetime of P* suggest that the maximum electron transfer rate P* {yields} H{sub M} is about 5 {times} 10{sup 9} sec{sup {minus}1} ({tau}{sub M} = 200 ps). This corresponds to a k{sub L}/k{sub M} ratio of at least 200. This large value of the branching ratio is remarkable in view of the structural symmetry of the reaction center. 13 refs., 2 figs.
- Research Organization:
- Argonne National Lab., IL (USA)
- Sponsoring Organization:
- DOE/ER
- DOE Contract Number:
- W-31109-ENG-38
- OSTI ID:
- 5656471
- Report Number(s):
- CONF-8908117-3; ON: DE89017676
- Resource Relation:
- Conference: 8. international congress on photosynthesis, Stockholm (Sweden), 6-11 Aug 1989
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
ELECTRON TRANSFER
RHODOPSEUDOMONAS
PHOTOSYNTHETIC REACTION CENTERS
BACTERIA
EXCITED STATES
MOLECULAR STRUCTURE
PHOTOSYNTHETIC MEMBRANES
TEMPERATURE DEPENDENCE
ENERGY LEVELS
MEMBRANES
MICROORGANISMS
400201* - Chemical & Physicochemical Properties