DEGRADATION OF PHOTOSYSTEM-II REACTION-CENTER D1-PROTEIN INDUCED BY UVB RADIATION IN ISOLATED THYLAKOIDS - IDENTIFICATION AND CHARACTERIZATION OF C-TERMINAL AND N-TERMINAL BREAKDOWN PRODUCTS

The effects of UVB radiation on the stability of Photosystem II reaction center D1-protein in isolated thylakoids are investigated. A new C-terminal degradation product has been identified and characterized, produced by cleavage in the second transmembrane segment. Immunological evidence for the presence of N-terminal fragments corresponding to the remaining part of D1-protein is also provided. The appearance of these fragments is not affected by lowering the temperature from 22 degrees C to 4 degrees C, changing the pH from 6 to 8, adding soybean trypsin inhibitor or excluding oxygen from the thylakoid suspension.