Separation of the Photosystems with Retention of their Photochemical Activities

Abstract

Inside-out vesicles enriched in photosystem (PS) II activity have been isolated by phase-partitioning in a aqueous two phase system (Åkerlund et al. 1976). We have modified the procedure to obtain a clean separation of the photosystems. Moreover, the PS II vesicles herein obtained were of simple polypeptide composition with retained oxygen evolving activity (Henry, Møller 1981). The necessary modifications entailed:

• (i) Membrane stacking in the presence of 5–10 mM MgC1₂ to assure a more efficient stacking compared to that obtained with 150 mM NaCl used in the original procedure. The necessity of stacked membranes for the formation of inside-out vesicles has been demonstrated (Anderson et al. 1978).

• (ii) Membrane disruption at higher pressures achieved by the use of a French Pressure Cell and repetition of the pressure treatments.

• (iii) An increase in the number of phase partitioning cycles resulting in a preparation of higher purity.

• (iv) Optimization of the composition of the phase-partitioning system to produce oxygen evolving PS II vesicles with a minimum number of polypeptides.