Pigment Content and EPR Characterization of the Photochemical Reaction Center of Photosystem II

The reaction center of Photosystem II (PS II) is comprised of the D1 and D2 polypeptides which bind some of the cofactors necessary for photochemical charge separation and secondary electron transfer. A complex of these polypeptides and cyt b559 has been isolated from PS II membranes, either with Triton X-100 [1], or a combination of LiClO4 and dodecylmaltoside [2]. A comparison between the two isolation methods revealed that the dodecylmaltoside complex (DM-complex) is more stable [2] and contains approximately 30% more pigment than the Triton X-100 complex (TX-complex) [3]. The DM-complex can be isolated with high yield, without significant loss of b559; therefore, the number of pigments can be estimated by comparing b559 contents in DM-complexes and in well-characterized PS II membranes [4] or reaction center complexes [5]. From such a comparison it was concluded that the DM-complex contains 10–12 Chl a, 2–3 Pheo a and 2 b559 molecules [3].