Removal of nuclear contaminants and of non-specifically photosystem II-bound copper from photosystem II preparations

In conventional photosystem II preparation high amounts of Cu are found. After fractionation by centrifugation, Cu can be completely removed from photosystem II without affecting either its photosynthetic activity or the composition of its specific proteins. We could demonstrate that the Cu was associated with nuclear contaminants in the starch fraction. Among the contaminants, several histones were identified by specific antisera and by N-terminal sequencing. In order to obtain homogeneous BBY preparations of PSII a procedure is employed that involves a 10000 g centrifugation step and which eliminates non-specifically bound metals, nucleic acids and histones with the starch pellet. The resulting starch-free BBY (BBY_s-), which is free of these nuclear contaminants, is an appropriate preparation for biophysical studies or for those of metal interactions with PSII.