Methods to prepare photosystem (PS)I reaction center (RC) subunit polypeptides are described. For PsaC, PsaD, PsaE, and PsaY, the filtrate resulting from the ultrafiltration in Chapter 6 is used for preparative sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). PsaA and PsaB, Type II PSI particles, prepared as described in the preceding chapter, are treated with sodium dodecyl sulfate, then applied on preparative SDS-PAGE. After electrophoresis, each band is cut out and electroeluted. A simple method to prepare PsaC is also presented.