Lifetimes of photosystem i and II proteins in the cyanobacterium Synechocystis sp. PCC 6803

The half-life times of photosystem I and II proteins were determined using ¹⁵N-labeling and mass spectrometry. The half-life times (30-75 h for photosystem I components and <1-11 h for the large photosystem II proteins) were similar when proteins were isolated from monomeric vs. oligomeric complexes on Blue-Native gels, suggesting that the two forms of both photosystems can interchange on a timescale of <1 h or that only one form of each photosystem exists in thylakoids in vivo. The half-life times of proteins associated with either photosystem generally were unaffected by the absence of Small Cab-like proteins.