Electrons generated by photosystem II are utilized by an oxidase in the absence of photosystem I in the cyanobacterium Synechocystis sp. PCC 6803.
The reduction and reoxidation kinetics of the first quinone-type electron acceptor in photosystem II, QA-, were measured by fluorescence in a light-tolerant, photosystem I-less strain of the cyanobacterium Synechocystis sp. PCC 6803. In this strain, which shows excellent amplitudes of variable fluorescence, the rate of QA- oxidation after photoreduction of the plastoquinone pool was about half of that in the presence of photosystem I. However, upon addition of 5 mM KCN, QA- decay was very slow, and the rate was comparable to that seen in the presence of diuron, which blocks electron transport between QA and QB. The KCN-imposed block of QA- oxidation was removed efficiently by addition of exogenous quinones that can oxidize the plastoquinone pool. These results indicate that, in the absence of photosystem I, photosystem II-generated electrons are used very effectively by an oxidase located in the thylakoid; this oxidase may be a component of the respiratory chain.
Vermaas
W F
WF
Department of Biochemistry, Arrhenius Laboratories for Natural Sciences, Stockholm University, Sweden.
Shen
G
G
Styring
S
S
D000458:Cyanobacteria / Q000201:enzymology*; D004237:Diuron / Q000494:pharmacology; D004579:Electron Transport / Q000187:drug effects; D007700:Kinetics; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000378:metabolism*; D045322:Photosynthetic Reaction Center Complex Proteins / Q000378:metabolism*; D045331:Photosystem I Protein Complex; D045332:Photosystem II Protein Complex; D011190:Potassium Cyanide / Q000494:pharmacology; D011809:Quinones / Q000378:metabolism; D013050:Spectrometry, Fluorescence
D045322:Photosynthetic Reaction Center Complex Proteins; D045331:Photosystem I Protein Complex; D045332:Photosystem II Protein Complex; D011809:Quinones; D004237:Diuron; D010088:Oxidoreductases; D011190:Potassium Cyanide