Uphill energy transfer in a chlorophyll d-dominating oxygenic photosynthetic prokaryote, Acaryochloris marina

The steady-state fluorescence properties and uphill energy transfer were analyzed on intact cells of a chlorophyll (Chl) d-dominating photosynthetic prokaryote, Acaryochloris marina. Observed spectra revealed clear differences, depending on the cell pigments that had been sensitized; using these properties, it was possible to assign fluorescence components to specific Chi pigments. At 22 degrees C, the main emission at 724 nm came from photosystem (PS) II Chi LJ, which was also the source of one additional band at 704 nm. Chi a emissions were observed at 681 nm and 671 nm. This emission pattern essentially matched that observed at -196 degrees C. as the main emission of Chi d was located at 735 nm, and three minor bands were observed at 704 nm, 653 nm, and 667 nm, originating from Chi d Chi a, and Chi a, respectively. These three minor bands, however, had not been sensitized by carotenoids, suggesting specific localization in PS II. At 22 degrees C, excitation of the red edge of the absorption band (which, at 736 nm, was 20 nm longer than the absorption maximum): resulted in fluorescence bands of Chi d at 724 nm and of Chi a at 682 nm, directly demonstrating an uphill energy transfer in this alga. This transfer is a critical factor for in vivo activity, due to an inversion of energy levels between antenna Chi d and the primary electron donor of Chi a in PS II. (C) 2000 Elsevier Science B.V. All rights reserved.