the side-chain by spinach ferredoxin:
NADP+ oxidoreductase (FNR) in the presence of NADPH has been studied. Both NADPH oxidation and oxygen uptake due to plastosemiquinone autoxidation were highly stimulated only in the presence of sodium cholate among the used detergents.
Sodium cholate at the concentration of 20 mMwas found to be the most effective on both PQ-4 and PQ-9-mediated oxygen uptake.
The FNR-dependent reduction of plastoquinones incorporated into sodium cholate micelles was stimulated by spinach ferredoxin
but inhibited by Mg2+ ions. It was concluded that the structure of sodium cholate micelles facilitates contact of plastoquinone
molecules with the enzyme and creates favourable conditions for the reaction similar to those found in thylakoid membranes for
PQ-9 reduction. The obtained results were discussed in terms of the function of FNR as a ferredoxin:plastoquinone reductase both
in cyclic electron transport and chlororespiration.