Abstract
State transition in oxygenic photosynthesis is a short-term mechanism of excitation energy redistribution between photosystem I (PSI) and II (PSII). It is hypothesized that preferential excitation of PSII translocates mobile light-harvesting complex from PSII to PSI. Although there are several LHCII polypeptides in higher plants and algae, biochemical evidence for which types of LHCII polypeptides are mobile, is weak. Here, using the green alga Chlamydomonas reinhardtii cells locked into state 1 and state 2, we established the procedure to separate chlorophyll-protein complexes under a mild condition and found a new PSI-LHCI supercomplex specifically from state 2 cells which is larger than the normal supercomplex and contains the mobile LHCII polypeptides. These mobile polypeptides were identified as CP26, CP29 and LHCII TypeII by mass spectroscopic and immunochemical analyses. A molecular mechanism on the translocation of LHCII complexes between PSI and II during state transition will be discussed.
