Functional characteristics of chlorophyll d-predominating photosynthetic apparatus in intact cells of Acaryochloris marina.

Functional organization of the photosynthetic apparatus in the unique chlorophyll d-predominating prokaryote, Acaryochloris marina, was studied using polarographic measurements of single-turnover flash yields, action spectra and optical cross sections for PS-specific reactions. O(2) evolution was indicative of PS II activity, while reversible photoinhibition of respiratory O(2) uptake under aerobic conditions in the presence of DCMU and H(2) photoevolution by anaerobically adapted cells were the indicatives of PS I activity. O(2) evolution in the cells upon single-turnover flashes followed the normal S-state cycle with a period-4 oscillation. Analysis of action spectra for the partial reactions of photosynthesis revealed that: (1) distinct spectral forms of Chl d are nonuniformly distributed between PS I and PS II, e.g. Chl d-695 and Chl d-735 are preferentially located in PS II and PS I, respectively; (2) a minor fraction of Chl a in the cells belongs mostly to PS II; (3) biliproteins transfer excitation energy both to PS II and, with a lower efficiency, PS I; (4) the efficiency of energy transfer from biliproteins to PS II depends on the light quality growth conditions and is larger in white light (WL)-grown cells compared to the red light (RL)-grown cells. Content of functional O(2) evolving PS II centers decreases 2 times in the RL-grown cells relative to the WL-grown cells, whereas content of competent PS I centers involved in photoinhibition of respiration remains almost the same in both the cultures. The effective antenna size of PS I was estimated to be 80-90 Chl d including 3-10 molecules absorbing at 735 nm. The effective optical cross-section of PS II corresponded to 90-100 Chl d and, presumably, 4 Chl a + 2 Pheo a [Mimuro et al. (1999) Biochim Biophys Acta 1412: 37-46]. Optical cross-section measurements indicated that the functional PS II units of A. marina attach one rod of four hexameric units of biliproteins.