A photosystem II reaction center complex containing D-1 and D-2 polypeptides and cytochrome b-559 was isolated from spinach grana thylakoids using ion-exchange chromatography. The complex contains five chlorophyll a molecules, two pheophytin a molecules, one β-carotene, and one or two cytochrome b-559 heme molecules. It exhibits a reversible absorbance change indicative of reduced pheophytin accumulation, suggesting that the primary charge separation in photosystem II occurs at the D-1 and D-2 subunit heterodimer. The study confirms that the D-1 and D-2 subunits, along with cytochrome b-559, form a pigment-protein complex. The complex was purified and characterized using various techniques, including gel electrophoresis and HPLC. The results support the hypothesis that the D-1 and D-2 subunits play a role similar to the L and M subunits in bacterial reaction centers. The complex is active in the photoreversible accumulation of reduced pheophytin, indicating that it is the site of primary charge separation in photosystem II. The study also highlights the importance of cytochrome b-559 in the photosystem II reaction center, although its exact function remains unclear. The research provides experimental evidence supporting the role of D-1 and D-2 subunits in photosystem II.A photosystem II reaction center complex containing D-1 and D-2 polypeptides and cytochrome b-559 was isolated from spinach grana thylakoids using ion-exchange chromatography. The complex contains five chlorophyll a molecules, two pheophytin a molecules, one β-carotene, and one or two cytochrome b-559 heme molecules. It exhibits a reversible absorbance change indicative of reduced pheophytin accumulation, suggesting that the primary charge separation in photosystem II occurs at the D-1 and D-2 subunit heterodimer. The study confirms that the D-1 and D-2 subunits, along with cytochrome b-559, form a pigment-protein complex. The complex was purified and characterized using various techniques, including gel electrophoresis and HPLC. The results support the hypothesis that the D-1 and D-2 subunits play a role similar to the L and M subunits in bacterial reaction centers. The complex is active in the photoreversible accumulation of reduced pheophytin, indicating that it is the site of primary charge separation in photosystem II. The study also highlights the importance of cytochrome b-559 in the photosystem II reaction center, although its exact function remains unclear. The research provides experimental evidence supporting the role of D-1 and D-2 subunits in photosystem II.