Evidence for two active branches for electron transfer in photosystem I

Mariana Guergova-Kuras, Brent Boudreaux, Anne Joliot, Pierre Joliot, Kevin Redding

Research output: Contribution to journalArticlepeer-review

279 Scopus citations


All photosynthetic reaction centers share a common structural theme. Two related, integral membrane polypeptides sequester electron transfer cofactors into two quasi-symmetrical branches, each of which incorporates a quinone. In type II reaction centers [photosystem (PS) II and proteobacterial reaction centers], electron transfer proceeds down only one of the branches, and the mobile quinone on the other branch is used as a terminal acceptor. PS I uses iron-sulfur clusters as terminal acceptors, and the quinone serves only as an intermediary in electron transfer. Much effort has been devoted to understanding the unidirectionality of electron transport in type II reaction centers, and it was widely thought that PS I would share this feature. We have tested this idea by examining in vivo kinetics of electron transfer from the quinone in mutant PS I reaction centers. This transfer is associated with two kinetic components, and we show that mutation of a residue near the quinone in one branch specifically affects the faster component, while the corresponding mutation in the other branch specifically affects the slower component. We conclude that both electron transfer branches in PS I are active.

Original languageEnglish (US)
Pages (from-to)4437-4442
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Issue number8
StatePublished - Apr 10 2001
Externally publishedYes

ASJC Scopus subject areas

  • General


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