Title: Interaction between electron transport components in chloroplasts
Abstract: The relative concentrations of the electron carriers between the two photosystems and their interactions were studied in isolated chloroplasts. 1. By monitoring the redox states of P700 and cytochrome f we determined relative concentrations of 12:1:1 for the Photosystem II electron acceptor pool (Q + A), cytochrome f and P700, respectively. In addition we accounted for a third, unidentified component ("Pc"), associated with Photosystem I, possibly plastocyanin, of approximately the same pool size as P700. We thus observed 15 electron equivalents in the electron transport chain between the photoacts, 12 on the System-II and 3 on the System-I side of the rate-limiting step. 2. Apparent equilibrium constants were determined from observations of the redox states of cytochrome f and P700 (KCyt,f-P700) and of "Pc" and P700 (K"Pc"-P700) under various conditions. The behavior of the "Pc"-P700 system was symmetrical during reduction in darkness and photo-oxidation by far-red light suggesting a true equilibrium K"Pc"-P700 ⋍20 (ΔE′0′ ⋍80 mV). The interaction between cytochrome f and P700 proved complex, suggesting a high equilibrium constant in dark and low values in the light (KCyt.f-P700 ⋍5–10). 3. The cytochrome f-P700 data were compatible with non-interacting three-component reaction chains: cytochrome f→ "Pc" → P700 or cytochrome f→ P700 ← "Pc". This model, however, did not fit the observed interactions between "Pc" and P700. These results, like earlier observations of the overall system (Q → P)4 suggest a light-induced change in the properties of the reaction chain.
Publication Year: 1970
Publication Date: 1970-12-01
Language: en
Type: article
Indexed In: ['crossref', 'pubmed']
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Cited By Count: 63
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