En savoir plus

Reductive carbon fixation consumes NADPH, which is regenerated by the enzyme ferredoxin:NADP(H) oxidoreductase (FNR) using electrons excited at photosystem I. Our previous work indicates that in angiosperms, this enzyme is always associated with the thylakoid membrane, but switches between tightly bound and loosely bound forms in response to illumination. We have also found that, under some conditions, the tightly bound form is important for an alternative electron transport pathway that returns electrons to the quinone pool (cyclic electron transport), rather than reducing NADPH. When FNR was discovered in the 1970s, it was reported by several groups that activity was higher when the enzyme was tightly bound to the membrane. Later, the membrane tether proteins that anchor FNR to the thylakoid in its “tight” membrane binding form were discovered. Confusingly, the authors reported that this interaction had no effect on FNR activity. We have combined plant genetics and protein film electrochemistry to dissect the impact of FNR:tether interactions on catalysis. In doing so we have resolved this contradiction and I will describe what we have discovered about the regulatory mechanism, and the implications of this for photosynthetic electron transport.