Degradation of psaB gene product, the reaction center subunit of photosystem I, is caused during photoinhibition of photosystem I: Possible involvement of active oxygen species

Specific degradation of psaB gene product, one of the two large subunits of photosystem I (PS I) reaction-center, was observed during photoinhibition of PS I. In the in vitro photoinhibition using spinach thylakoid membranes, the degradation of psaB gene product gave rise to fragments of 51 kDa and 45 kDa. n-Propyl gallate, a scavenger of active oxygen species, suppressed the generation of these fragments. Addition of methyl viologen, which protects PS I from photoinhibition but increases the production of superoxide, suppressed the generation of 51 kDa fragment but increased the generation of 45 kDa fragment. It was concluded that interaction of active oxygen species with reduced electron acceptor in PS I results in inactivation of PS I and in generation of 51 kDa fragment. On the other hand, 45 kDa fragment was generated solely by the presence of active oxygen species independent of the inhibition of PS I activity.