Isolation and characterization of photosystem II core complexes with high oxygen evolution activity from spinach using the non-ionic detergent 6-O-(N-heptylcarbamoyl)-methyl-α-D-glucopyranoside

Two different kinds of oxygen evolving photosystem II (PSII) core complexes were isolated in the present study by solubilization of PSII enriched thylakoid membranes from spinach with the non-ionic detergent 6-O-(N-heptylcarbamoyl)-methyl-(alpha)-D-glucopyranoside (Hecameg) under different conditions. The PSII core complex isolated at higher ionic strength was similar to that isolated by using octyl-beta-D-glucopyranoside (OGP) and lacked the 23 and 17 kDa extrinsic proteins of the oxygen evolving complex but retained the 22 kDa PsbS protein. Solubilization of the PSII membranes with Hecameg at lower ionic strength allowed the isolation of another PSII complex that retained all the three extrinsic proteins (33, 23 and 17 kDa) of the oxygen evolving complex but was depleted of the 22 kDa PsbS protein. This complex exhibited high rates of oxygen evolution and was found to be more sensitive to DCMU indicating a better structural and functional integrity and may be treated as the minimal functional unit required for PSII photochemistry. The detergent Hecameg is relatively inexpensive and the methodology remains simple since it does not require any chromatography or density gradient ultracentrifugation.