AI Article Synopsis
- The absorbance changes of ferredoxin in thylakoids indicate the activity of the enzyme ferredoxin-plastoquinone reductase (FQR) in cyclic electron transport.
- Under anaerobic conditions, light causes a decline in absorbance tied to plastoquinone oxidation, and when light is off, ferredoxin is reoxidized, allowing measurement of the cyclic electron transport rate.
- FQR activity is affected by classical inhibitors like antimycin and others, suggesting a separate quinone reduction site outside the cytochrome bf complex, with potential involvement of ferredoxin-NADP(+) reductase in FQR activity, although NADPH2 surprisingly inhibits FQR.
Article Abstract
Absorbance changes of ferredoxin measured at 463 nm in isolated thylakoids were shown to arise from the activity of the enzyme ferredoxin-plastoquinone reductase (FQR) in cyclic electron transport. Under anaerobic conditions in the presence of DCMU and an appropriate concentration of reduced ferredoxin, a light-induced absorbance decrease due to further reduction of Fd was assigned to the oxidation of the other components in the cyclic pathway, primarily plastoquinone. When the light was turned off, Fd was reoxidised and this gave a direct quantitative measurement of the rate of cyclic electron transport due to the activity of FQR. This activity was sensitive to the classical inhibitor of cyclic electron transport, antimycin, and also to J820 and DBMIB. Antimycin had no effect on Fd reduction although this was inhibited by stigmatellin. This provides further evidence that there is a quinone reduction site outside the cytochrome bf complex. The effect of inhibitors of ferredoxin-NADP(+) reductase and experiments involving the modification of ferredoxin suggest that there may be some role for the reductase as a component of FQR. Contrary to expectations, NADPH2 inhibited FQR activity; ATP and ADP had no effect.
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| http://dx.doi.org/10.1007/BF00029815 | DOI Listing |
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