2011). The kinetics were also KPT-8602 simulated using coarse-grained modeling and the obtained parameters were used to illustrate various aspects of PSII functioning
(Caffarri et al. 2011). It was for instance calculated that for the largest supercomplex the efficiency of charge separation is 89 %. In the presence of one open and one closed RC, the photochemical efficiency reduces to 78 %, which is much larger than the value of 45 % calculated when the cores are not connected into dimers. This demonstrates that a dimeric conformation increases the light-harvesting capacity by more than 70 % in the presence of one closed RC. This is an important property for PSII because of its slow turnover and it also suggests that the arrays of PSII that are observed in electron-microscopy measurements GDC-0068 concentration are advantageous when a substantial fraction of the RC’s is closed. In fact, the advantage
of PSII units being connected to each other was already discussed many decades ago and it was experimentally determined that indeed many “photosynthetic units” (PSU’s) are connected to each other (see e.g., (Clayton 1981)). Two popular models from those days were the puddle model, in which PSU’s were not connected and the lake model, in which basically all PSU’s were connected. Whereas for purple bacteria, the lake model is applicable, it was found that for plants, the situation was somewhere in between these extreme models (see e.g., also (Clayton 1981)), which is in agreement with the organization observed with electron-microscopy (see above). Energy transfer and charge separation in PSII membranes Grana membranes Selleck CB-839 can be purified (the so-called BBY particles) that contain practically only PSII complexes (Berthold et al. 1981; Dunahay et al. 1984;
Albertsson et al. 1981), although it is not completely understood how PSII is organized in these membranes. over It had been suggested that C2S2 represents the supercomplex in high light, while C2S2M2 is the result of low-light growth (Daum et al. 2010). However, it was recently demonstrated that also in high light, C2S2M2 is still the main supercomplex in Arabidopsis (Kouril et al. 2012). In high light, the amount of LHCII trimers is lower than in low light, although in all cases the stoichiometry LHCII/core is higher than two (it is often between three and four) (Bailey et al. 2001; Anderson and Andersson 1988; Kouril et al. 2012), meaning that not all LHCII trimers are present in the supercomplexes but that there are also “extra” trimers. The location of these “extra” LHCII trimers, however, is still unknown and some of them might be located in the LHCII-only domains that were proposed by Boekema et al. (Boekema et al. 2000) although it should be emphasized that most of the “extra trimers” should be connected to PSII which is not necessarily the case for these LHCII-only domains.