Isolation of a Photosystem II Reaction Center Consisting of γ and δ Subunits (D-1 and D-2) and Cytochrome b-559

Abstract

It is well known that the PS II reaction center of oxygenic photosynthetic organisms is contained in a chlorophyll-protein complex consisting of six polypeptides; α, β, γ, δ subunits (1) and two polypeptides of cytochrome b-559 (2). However, there is a controversy concerning the localization of the site of primary charge separation in the complex (3–8). Some evidence supports the proposal that the α subunit is the site of the primary photochemistry (3–6). However, the amino acid sequence homology between the γ and δ subunits and the L and M subunits from purple photosynthetic bacteria has led to a proposal (7,8) that the γ and δ subunits play a role in the PS II reaction center similar to that of the L and M subunits in the bacterial reaction center whose structure has been recently determined by x-ray crystallographic analysis (9).