Relationships between heterogeneity of the PSII core complex from grana particles and phosphorylation

Isoelectrofocusing of photosystem II enriched membranes from spinach reveals the presence of at least four different populations of PSII core complex. The four bands are neither equally populated nor equally active in electron transport from diphenylcarbazide to 2,6-dichlorophenolindophenol. Under conditions of a low and high phosphorylation level a change in the relative populations of the PSII core isoforms is observed and the amount of radiolabelled phosphate incorporated into the four types of complexes is correlated to the value of their isoelectric point suggesting that the origin of the heterogeneity evidenced in vitro is at least partially due to different levels of light-induced phosphorylation. A 9 KD phosphoprotein, previously described in PSII, is found in our core complex preparation at a concentration which decreases as the total phosphorylation level on D1/D2 polypeptides increases.