The PSI‐E subunit of photosystem I binds ferredoxin:NADP+ oxidoreductase

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Abstract
A photosystem I complex containing the polypeptides PSI‐A to PSI‐L, light‐harvesting complex I and ferredoxin:NADP+ oxidoreductase has been isolated from barley using the non‐ionic detergent n‐decyl‐β‐d‐maltopyranoside. The ratio between bound forredoxin:NADP+ oxidoreductase and P700 is 0.4 ± 0.2. The complex is highly active in catalyzing light‐induced transfer of electrons from plastocyanin to NADP+ at rates of 280±150 and 1800 ± 800, μmol NADPH/(mg chl h), without and in the presence of saturating amounts of exogenously added ferredoxin:NADP+ oxidoreductase, respectively. Endogenously bound ferredoxin:NADP+ oxidoreductase interacts with the PSI‐E subunit as demonstrated by cross‐linking experiments using two different types of cross‐linkers and identification of the products by Western blotting and the use of monospecific antibodies.