Identification and characterization of D1 and D2 protein breakdown fragments in cotyledon thylakoids from Ceratonia siliqua L.

Breakdown products of Photosystem II reaction centre D1 and D2 proteins have been detected and characterized in cotyledon thylakoids from the epigeal species Ceratonia siliqua. Breakdown fragments are mainly localized in the stroma-exposed membranes. Cleavage of D1 protein occurs in the hydrophylie loop connecting the 4th and 5th putative transmembrane segments, giving rise to fragments very similar, if not identical, to those observed during light-induced turnover or photoinhibition. Fragments from D2 protein originate from cleavage somewhere between the 3rd and 4th transmembrane segments.