Some 20 fungi species may possess an energy-generating proton pump never before seen outside prokaryotes, scientists report in this week's PNAS. The investigators suggest the system could be widely spread among lower eukaryotes.

"The most surprising thing for me is that the fungi have kept this primitive energy pathway even though they possess normal respiration," said coauthor Leonid Brown, of the University of Guelph in Canada.

Eukaryotes are classically thought to create proton gradients for energy via respiration and chlorophyll. Over the last 30 years, scientists have found that archaea and eubacteria possess another form of photosynthesis, where bacteriorhodopsin-like membrane proteins drive light-driven translocation of protons. Homologous rhodopsins examined in eukaryotes until now apparently only had photosensory functions.

In the current study, Brown and colleagues analyzed the fungus Leptosphaeria maculans opsin gene and found a high degree of homology with bacteriorhodopsin. After expressing the opsin in membranes of...

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