Up-Hill Energy Transfer in LH1+LH2 Purple Bacteria

Abstract

The photosynthetic apparatus of purple bacteria consists of so-called core light harvesting complexes (LH1) which are intimately associated with a photochemical reaction centre (RC) and, in many cases, additional peripheral LH2 complexes. These peripheral complexes are comprised of antenna pigments with blue-shifted absorption compared to those of the core complexes. The absorption of light energy by the peripheral antenna system creates excited states (excitons) that then proceed energetically downhill, from the peripheral to the core complexes. However, in the cyanobacterium Synechococcus sp. (formerly Anacystis nidulans) [6], plant photosystem (PS) II [1] and the purple bacterium Rhodobacter (Rb.) sphaeroides [5] it was shown that the reverse back-transfer or uphill process is also possible. To date, the extent of this uphill transfer process in the purple bacteria has not been studied extensively and is open to debate.