HETEROGENEITY IN PHOTOSYSTEM-I - THE LARGER ANTENNA OF PHOTOSYSTEM-I-ALPHA IS DUE TO FUNCTIONAL CONNECTION TO A SPECIAL POOL OF LHCII

Thylakoids from spinach were fragmented by sonication and separated by aqueous two-phase partitioning into grana originating vesicles (alpha vesicles) and stroma membrane originating vesicles (beta vesicles) (Andreasson et al. (1988) Biochim. Biophys. Acta 936, 339-350). PS Ialpha and PS Ibeta were isolated from these two vesicle populations respectively, and their properties were compared. PS Ialpha contains more of light harvesting complex II (LHCII) than PS Ibeta. The LHCII is functionally connected to PS I, a connection which is abolished by addition of octyl glucoside. The grana-derived alpha vesicles were further fragmented by sonication and separated by aqueous two-phase partitioning into vesicles enriched in margins and vesicles enriched in PS IIalpha from the center of the grana. By non-denaturating isoelectric focusing it was found that the LHCII pattern of PS Ialpha was almost identical to that of LHCII of the margin enriched vesicles but very different from that of LHCII associated with PS IIalpha. It is concluded that: (1) PS Ialpha (originating from grana membranes) has a larger functional antenna size than PS Ibeta (originating from stroma membranes) because of association with LHCII; (2) PS Ialpha is located in the periphery of the grana (margins and end membranes) and associated with a different pool of LHCII compared to that associated with PS IIalpha of the more central core of the grana.